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The  Effect  of  Organic  and  Inorganic  "Ad 
dition-Agents"  upon  the  Electro-Deposi- 
tion of  Copper  from  Electrolytes 
Containing  Arsenic 


BY 

CHING  YU  WEN 


SUBMITTED  IN  PARTIAL  FULFILMENT  OF  THE  REQUIREMENTS  FOR 

THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  IN  THE  FACULTY 

OF  PURE  SCIENCE,  COLUMBIA  UNIVERSITY 


PRESS  OF 
THE  NEW  ERA  PRINTING  COMPANY 


1911 


The  Effect  of  Organic  and  Inorganic  "Ad- 
dition-Agents" upon  the  Electro-Deposi- 
tion of  Copper  from  Electrolytes 
Containing  Arsenic 


BY 


CHING  YU  WEN 


SUBMITTED  IN  PARTIAL  FULFILMENT  OF  THE  REQUIREMENTS  FOR 

THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  IN  THE  FACULTY 

OF  PURE  SCIENCE,   COLUMBIA  UNIVERSITY 


PRESS  OF 

THE  NEW  ERA  PRINTING  COMPANY 

1911 


ACKNOWLEDGMENT. 

1  wish  to  express  my  profound  gratitude  to  Professor  Arthur 
L.  Walker  for  his  kind  advice;  and  I  am  especially  indebted  to 
Dr.  Edward  F.  Kern,  under  whose  direction  this  research  was 
conducted,  for  his  invaluable  suggestions  and  criticisms. 


.3 

226926 


INTRODUCTION. 

In  the  production  of  good  and  pure  copper  by  electrolysis,  the 
composition  of  the  electrolyte  is  one  of  the  important  factors. 
The  causes  of  poor  copper  deposits  are  chiefly  due  to  the  impuri- 
ties which  accumulate  in  the  electrolyte,  and  which,  under  usual 
conditions,  are  precipitated  along  with  the  copper.  Of  those  im- 
purities, the  most  harmful  and  troublesome  ones  are  arsenic  and 
antimony,  the  presence  of  which  in  the  deposited  copper  makes  it 
brittle  and  nodular.  It  has  been  a  known  fact  that  during  elec- 
trolysis, part  of  the  arsenic  and  antimony  contained  in  the  anode 
dissolves  and  remains  in  solution.  These  two  elements,  espe- 
cially the  arsenic,  are  allowed  to  accumulate  in  the  electrolyte  till 
a  critical  point  is  reached,  which  has  not  yet  been  definitely  de- 
termined. When  this  point  is  passed,  they  begin  to  be  deposited 
with  the  copper  on  the  cathode  and  render  the  deposit  bad  and 
brittle.  To  prevent  this,  it  is  therefore  of  utmost  importance  to 
maintain  the  electrolyte  within  a  certain  degree  of  purity,  in  other 
words,  to  keep  the  amount  of  arsenic  and  antimony  in  the  elec- 
trolyte below  the  critical  point.  This  is  usually  accomplished  in 
practice  by  withdrawing  a  certain  portion  of  the  electrolyte  and 
replacing  it  with  an  equal  quantity  of  fresh  solution,  and  the 
copper  in  the  impure  electrolyte  recovered  either  by  crystalliza- 
tion or  by  electrolysis  with  insoluble  lead  anodes.  This  not  only 
complicates  the  process  of  electrolytic  refining  of  copper,  but  also 
entails  an  extra  item  of  expenditure  in  the  production  of  electro- 
lytically  refined  copper. 

Another  thing  that  is  observed  during  the  electrolysis  is  that 
"  sprouts  "  or  dendritic  "  trees  "  often  form,  especially  along  the 
edges  of  the  cathode.  The  formation  of  such  "  trees  "  interferes 
with  the  work,  renders  it  more  difficult  to  operate,  and  prevents 
the  electrodes  from  being  placed  close  together ;  as  there  is  danger 
that  the  electric  current  would  be  short-circuited.  In  conducting 
the  electrolysis  in  a  commercial  way,  the  removal  of  these  "  trees  " 
becomes  absolutely  necessary  and  is  usually  done  by  the  tank 
inspectors,  thus  increasing  the  cost  of  refining. 


ELECTROLYTES  CONTAINING  ARSENIC.  5 

The  object  of  the  present  investigation  is,  therefore,  twofold: 
first,  to  prevent  the  deposition  of  arsenic  and  antimony  on  the 
cathode,  and  second,  to  prevent  the  formation  of  dendritic 
"  trees."  This  problem  was  worked  out,  having  in  mind  the  pro- 
duction of  solid  and  smooth  deposits,  from  copper  electrolytes 
containing  high  percentages  of  arsenic,  by  means  of  organic  and 
inorganic  "  addition-agents." 


ABSTRACTS   OF   LITERATURE. 

In  reviewing  the  literature  regarding  both  organic  and  in- 
organic addition-agents  little  was  found. 

Kiliani1  was,  perhaps,  the  first  man,  who  had  conducted  sys- 
tematic experiments  to  investigate  the  behavior  of  impurities 
present  in  the  copper  anode,  and  to  study  the  effect  of  inorganic 
salts  on  the  character  of  the  copper  deposit.  For  the  latter  case 
he  used  an  electrolyte  containing  15  grams  of  copper  sulphate 
and  5  grams  of  sulphuric  acid,  in  100  c.c.  solution  with  a  current 
density  of  20  amperes  per  square  meter.  He  observed  the  fact 
that,  with  a  small  amount  of  tin  salt  in  the  electrolyte,  good 
smooth,  malleable  copper  was  produced  while,  in  the  case  when 
the  electrolyte  contained  no  tin  salt,  the  deposit  was  extremely 
bad  and  brittle.  He  noted  also  the  fact  that  the  presence  of  a 
small  amount  of  tin  in  the  anode  caused  the  potential  difference 
between  electrodes  to  be  greatly  reduced. 

W.  Borchers2  performed  experiments  with  the  object  of  pre- 
venting the  crystalline  growth  of  copper  on  the  deposit,  by  adding 
to  the  electrolyte  a  sufficient  amount  of  sodium  chloride,  or 
magnesium  chloride.  He  found,  however,  by  the  addition  of 
these  reagents,  only  a  diminution  of  the  evil  could  be  effected. 

H.  O.  Hoffman3  has  pointed  out  that  hydrochloric  acid  is  used 
in  practice  to  precipitate  the  antimony  in  the  electrolyte.  This 
is  accomplished  by  the  addition  of  a  sufficient  quantity  of  crude 
hydrochloric  acid  to  the  head  tank  to  maintain  0.04  gram  of 
chlorine  per  liter  in  solution.  The  hydrochloric  acid  reacts  with 
the  antimony  and  precipitates  it  as  oxychloride.  When  there  is 
deficiency  of  hydrochloric  acid  the  sample-plate  becomes  streaked, 
tarnished,  black  and  brittle. 

It   is   said   that   ammonium   sulphate4   has   been   used   in   the 

1  Berg  und  Huttenmannisches  Zeitung,  1885,  p.  249. 

2  W.  Borchers,  "  Electrolytic  Smelting  and  Refining,"  p.  206  (translated 
by  McMillan). 

3  T.  A.  I.  M.  E.,  1904,  Vol.  34,  p.  312. 

4T.  Ulke,  "Modern  Electrolytic  Copper  Refining,"   ist  ed.,  p.   18. 

6 


ELECTROLYTES  CONTAINING  ARSENIC.  7 

electrolyte  to  hinder  the  precipitation  of  arsenic  on  the  cathode, 
and  the  amount  usually  added  was  from  0.5  to  20  per  cent.  The 
addition  of  this  salt  decreases  the  conductivity  of  the  electrolyte. 

L.  W.  Wickes5  investigated  the  percentage  of  arsenic  which 
the  deposited  copper  would  contain  for  a  given  potential  between 
electrodes,  and  the  relation  between  variations  in  the  potential 
and  the  amount  of  arsenic  in  the  copper  deposited.  For  his 
experiments  he  used  anodes  containing  I  per  cent.,  2  per  cent., 
and  4  per  cent,  arsenic,  and  an  electrolyte  containing  75 
parts  of  water,  19  parts  of  copper  sulphate,  and  6  parts  sul- 
phuric acid,  by  weight,  and  also  an  electrolyte  of  the  same  com- 
position, but  containing  o.ioi  per  cent,  arsenic  in  the  form  of 
arsenic  acid.  The  experiments  were  conducted  with  0.4  volt,  0.6 
volt,  and  0.8  volt.  He  found  that  with  different  voltages  and  the 
same  percentage  of  arsenic  in  the  anode,  the  percentage  of 
arsenic  in  the  cathode  copper  was  practically  the  same  in  all 
cases,  and  that  the  greater  the  percentage  of  arsenic  in  the  anode, 
the  more  erratic  were  the  results.  The  conclusion  which  he  drew 
of  his  experimental  data  is  that  the  percentage  of  arsenic  in  the 
deposited  copper  is  not  a  function  of  the  potential  between  elec- 
trodes, but  of  the  degree  of  hydrolyzation  of  the  sulphate  of 
arsenic  in  the  electrolyte. 

Of  the  work  on  organic  addition-agents,  that  of  Edward  F. 
Kern  and  Royal  P.  Jarves6  should  be  mentioned.  They  conducted 
experiments  to  investigate  the  effect  of  the  presence  of  tannin, 
pyrogallol,  gelatine,  and  resorcinol  upon  the  density  and  coher- 
ence of  electrolytically  deposited  copper,  lead,  and  silver.  For 
their  experiments  on  copper  they  used  two  kinds  of  electrolyte, 
the  cupric  sulphate  and  the  cupric  fluo-silicate.  With  the  former 
electrolyte  which  contained  16  grams  of  cupric  sulphate 
CuSO4-5H2O)  and  4  grams  of  sulphuric  acid  (H2SO4)  per  100 
c.c.,  they  found  that  the  presence  of  tannin,  resorcinol  or  gelatine 
equally  caused  the  copper  to  deposit  more  smoothly.  The  de- 
posited copper  formed  at  30°  C.  was  better  than  that  at  20°  C. 
With  the  fluo-silicate  electrolyte,  which  contained  6.34  grams  of 
copper,  and  3.60  grams  of  free  hydro-fluo-silicic  acid  (H2SiF6) 

5E.M.  thesis,   Metallurgical  Library,    School  of   Mines,    Columbia  Uni- 
versity. 

8  School  of  Mines  Quarterly,  1909,  Vol.  30,  p.  119. 


8  ELECTRO-DEPOSITION  OF  COPPER  FROM 

per  100  c.c.,  they  observed  that  the  deposits  were  rendered 
brighter  and  more  smooth  by  the  presence  of  tannin,  pyrogallol, 
or  gelatine.  The  first  of  these  addition-agents  was  the  most 
effective  while  the  last  two  were  somewhat  less.  Better  results 
were  also  obtained  at  30°  C.  than  at  20°  C. 

In  regard  to  the  function  of  organic  addition-agents,  Edward 
F.  Kern7  has  also  performed  invaluable  experiments  for  which 
the  following  electrolytes  were  used : 

1.  Gupric    electrolytes,    which    consisted    of    cupric    sulphate, 

cuprous  chloride,  and  cupric  fluo-silicate. 

2.  Lead  electrolytes,  which  consisted  of  lead  nitrate,  and  lead 

fluo-silicate. 

3.  Silver   electrolytes,   which   consisted   of   silver   nitrate   and 

silver  fluo-silicate. 

The  organic  addition-agents  employed  were  gelatine  resorcinol, 
pyrogallol,  and  tannin.  With  the  results  of  his  experiments  he 
concluded  as  follows :  "  That  the  most  suitable  organic  addition- 
agents  for  copper,  lead,  and  silver  electrolytes  are  compounds  of 
the  benzene  ring  series,  which  have  a  large  number  of  adjoining 
hydroxyl  radicals ;  and  also,  the  greater  the  molecular  weight  of 
the  addition-agent,  in  other  words,  the  larger  the  numbers  of 
hydroxyls,  the  more  effective  it  is  in  producing  more  satisfactory 
results." 

"  If  it  is  the  hydroxyl  (and,  as  well,  the  amine)  radicals  of 
organic  addition-agents,  which  cause  deposits  to  form  denser, 
smoother  and  less  crystalline;  then,  no  doubt,  this  effect  may  be 
attributed  to  the  reducing  property  of  the  addition-agents.  This 
statement  was  suggested  by  recalling  a  general  rule  of  organic 
chemistry,  which  is :  '  The  most  easily  oxidizable  organic  com- 
pounds of  the  benzene  ring  series,  and  those  which  more  readily 
precipitate  metals  from  their  solutions,  are  compounds  which  con- 
tain the  largest  number  of  hydroxyl  or  amine  radicals ;  and  the 
compounds  which  are  most  easily  oxidized  are  those  in  which  the 
hydroxyl  and  the  amine  radicals  are  the  more  closely  grouped/  " 

From  his  experimental  data  and  the  above  generalizations  he 
has  deduced  a  theory  regarding  the  function  of  an  addition-agent, 
which  reads :  "  The  function  of  an  addition-agent  in  an  electrolyte 
is  to  maintain  a  reducing  menstruum  around  the  cathode,  which, 
in  turn,  causes  the  electro-deposit  to  form  denser  and  smoother." 

7  Tran.  Amer.  Elect.  Society,  1909,  Vol.  XV.,  p.  441. 


ELECTROLYTES  CONTAINING  ARSENIC.  9 

"  The  fact  that  the  consumption  of  organic  addition-agents  is  in 
proportion  to  the  amount  of  metal  deposited  is  an  evidence  of 
their  reducing  action.  And,  for  this  reason,  in  order  to  maintain 
the  deposition  of  smooth,  dense,  coherent  deposits,  the  organic 
addition-agent  must  be  added  in  definite  amounts,  to  electrolytes 
from  time  to  time." 

From  the  results  of  his  investigations  on  inorganic  addition- 
agents,  he  writes  as  follows :  "  The  deposits  formed  in  electrolytes, 
which  contain  alkali  or  alkaline  earth  salts,  are  generally  denser, 
smoother  and  less  crystalline  than  those  which  are  formed  in 
electrolytes  which  do  not  contain  these  salts.  This  is  the  case 
with  nickel  sulphate  and  nickel  chloride  electrolytes,  which  con- 
tain salts  of  sodium,  potassium,  or  magnesium.  The  formation 
of  smoother  and  less  crystalline  deposits  from  these  electrolytes 
may  be  attributed  to  the  reducing  action  of  the  sodium,  potassium, 
or  magnesium  ion  in  the  layer  of  electrolyte  which  surrounds  the 
cathode.  Ammonium  salts  act  similar  to  the  alkali  salts,  but  to 
a  less  marked  degree.  These  facts  also  seem  to  c6nform  to  the 
above  advanced  theory." 

Not  only  have  the  organic  and  inorganic  addition-agents  been 
found  to  improve  copper  deposits,  but  the  temperature,  of  the 
electrolyte  has  also  been  found  to  exert  a  marked  beneficial  influ- 
ence. The  investigations  of  Forster  and  Seidel8  have  shown  that 
the  deposits  produced  at  40°  C.  were  uniformly  crystalline  and 
possessed  great  ductility,  and  those  formed  at  60°  C.  were  less 
ductile  and  of  coarser  crystals.  They  have  also  shown  that  the 
deposits  formed  at  higher  temperatures  were  of  greater  tensile 
strength  than  those  formed  at  lower  temperatures. 

There  are  found  other  literatures  in  regard  to  the  addition- 
agents  in  electrolytes  of  lead,  silver,  and  nickel.  As  these  have 
nothing  to  do  with  the  present  investigation,  they  will  not  be  here 
discussed. 

*Zeitschrift  fur  Electro chemie,  1899,  Vol.  5,  p.  508. 


EXPERIMENTAL   PART. 

PREPARATION  OF  COPPER-ARSENIC  AND  COPPER-ANTIMONY 

ALLOYS. 

For  making  the  anodes,  alloys  of  copper-arsenic,  and  of  copper- 
antimony  were  first  prepared.  Ten  pounds  of  granulated  copper, 
covered  with  a  layer  of  charcoal,  were  first  melted  in  a  Dixon 
graphite  crucible  (no.  20)  in  a  gas-fired  furnace.  When  the 
copper  was  completely  melted,  it  was  thoroughly  poled  with  sticks 
of  wood.  The  crucible  was  then  taken  out  of  the  furnace,  and  to 
the  molten  copper  1.5  pounds  of  metallic  arsenic  wrapped  with 
copper  foil  was  added.  The  crucible  was  again  heated.  The 
molten  alloy  was  stirred  with  a  graphite  rod  so  as  to  secure  uni- 
form composition.  It  was  granulated  by  pouring  slowly  at  a 
vertical  distance  of  six  or  seven  feet  into  a  large  basin  full  of  cold 
water ;  depth  2  feet.  The  copper-antimony  alloy  was  made  in 
the  same  way  as  above,  except  that  0.5  pounds  of  antimony  was 
added  in  small  chunks  to  10  pounds  of  molten  copper. 

MAKING  OF  ANODES. 

Twelve  pounds  of  granulated  refined  copper  covered  with  a 
layer  of  charcoal  was  first  melted  in  a  Dixon  graphite  crucible  in 
a  gas-fired  furnace  and  poled  to  tough  pitch  as  described  in  the 
case  of  making  copper-arsenic  alloy.  Then  1.5  pounds  of  the 
copper-arsenic  alloy  and  2  pounds  of  copper-antimony  alloy  were 
mixed  and  added  to  the  molten  copper.  Having  been  thoroughly 
stirred  with  a  graphite  rod  it  was  cast  into  anodes  in  an  iron 
mould,  which  had  previously  been  warmed  and  painted  with  bone 
ash.  The  size  of  the  anodes  was  4^  inches  high,  2j  inches  wide, 
and  f  inch  thick 

A  small  portion  of  the  anode  copper  was  granulated  as  before 
and  taken  for  analysis  for  arsenic  and  antimony.  The  methods 
of  determining  these  two  metals  are  described  in  the  following. 

10 


ELECTROLYTES  CONTAINING  ARSENIC.  1 1 

DETERMINATION   OF  ARSENIC  AND  ANTIMONY   IN   ANODE  AND 
CATHODE  COPPER. 

Considerable  time  was  given  to  the  determination  of  arsenic  and 
the  separation  of  antimony  from  it  by  the  distillation  method,  for 
which  different  procedures  and  various  reducing  agents  were 
tried.  It  was  found  that  most  of  the  methods  ordinarily  used, 
particularly  the  reducing  agents,  did  not  give  satisfactory  results. 
The  adopted  standard  method  finally  worked  out  and  found  to 
be  successful  and  practical  may  be  described  as  follows : 

A  sample  of  about  10  grams,  in  the  case  of  anode  copper,  and 
from  30  to  100  grams,  in  the  case  of  cathode  copper,  depending 
upon  the  amount  of  arsenic  it  contained,  was  weighed  out  and 
dissolved  in  a  no.  6  breaker  with  concentrated  nitric  acid  (45  c.c. 
for  10  gm.  of  copper).  The  breaker  was  covered  with  a  watch 
glass  and  warmed  on  a  hot  plate  in  order  to  hasten  the  dissolution 
of  copper.  When  the  solution  was  complete,  the  beaker  was 
removed  from  the  hot  plate  and  about  I  gm.  of  ferrous  sulphate 
added.  The  beaker  was  again  heated  to  expel  the  red  fume: 
The  solution  was  then  diluted  to  400  or  500  c.c.  and  warmed. 
The  iron,  arsenic,  and  antimony  was  precipitated  with  strong 
ammonium  hydroxide.  Sufficient  excess  was  added  to  dissolve 
all  the  copper  compounds.  The  precipitate  was  allowed  to  settle, 
decanted,  filtered  while  still  warm  and  finally  washed  with  a  hot 
solution  of  ammonia  ( 10  water  to  i  ammonium  hydroxide,  sp. 
gr.  0.9).  The  precipitate,  together  with  the  filter  paper  was 
transferred  into  a  no.  I  beaker  covered  with  a  watch  glass,  and 
digested  gently  on  the  hot  plate  with  20  c.c.  of  concentrated  nitric 
acid,  until  practically  all  the  red  fume  was  driven  off.  (Care 
should  be  taken  not  to  heat  the  solution  vigorously  lest  some  of 
it  would  be  lost  by  spattering.)  After  cooling  the  solution,  10  c.c. 
of  concentrated  sulphuric  acid  was  added,  and  the  beaker  was 
re-heated  on  the  hot  plate  till  fume  of  sulphuric  anhydride  freely 
evolved.  It  was  then  allowed  to  cool  and  about  5  c.c.  of  a 
lO-per  cent,  solution  of  hypophosphorous  acid,  or  6  c.c.  of  a 
2O-per  cent,  solution  of  potassium  hypophosphite  was  added  (pro- 
vided the  solution  did  not  contain  more  than  0.3  of  a  gram  of 
arsenic).  The  solution  was  again  heated  on  the  hot  plate  until 
all  the  excess  of  the  hypophosphorous  acid,  or  potassium  hypo- 


12  ELECTRO-DEPOSITION  OF  COPPER  FROM 

phosphite  was  destroyed :  this  was  indicated  by  the  evolution  of 
strong  fume  of  sulphuric  anhydride.  (In  order  to  be  sure  of 
destroying  the  excess  of  the  reducing  agent,  let  it  fume  for  at 
least  one  half  an  hour.) 

The  content  in  the  beaker,  after  cooling,  was  transferred  into 
the  distilling  flask  (D,  Fig.  i),  the  beaker  was  then  rinsed  twice 
with  only  10  c.c.  of  water.  The  distilling  flask  was  gently  heated 
to  boiling,  with  a  smoky  flame,  in  order  to  expel  any  sulphurous- 
acid  gas  that  might  be  present  in  the  solution.  Bumping  of  the 
solution  sometimes  occurred  and  was  prevented  by  imparting  a 
rotary  motion  to  the  solution.  It  was  then  allowed  to  cool. 
After  cooling,  any  solution  that  was  left  in  the  beaker  was  rinsed 
into  the  distilling  flask  twice  or  three  times  with  30  c.c.  of  concen- 
trated hydrochloric  acid,  making  a  total  of  not  over  10  c.c.  water 
and  40  c.c.  concentrated  HCL  The  apparatus,  as  is  shown  in 
Fig.  i,  was  now  connected  and  adjusted;  the  receiver  R  (a  no.  4 
beaker),  containing  about  250  c.c.  of  water,  was  placed  in  a  bath 
of  cold  water,  B,  and  under  the  condenser,  C,  the  tip  of  which  was 
immersed  into  the  water  to  a  depth  of  about  J  inch.  Ten  c.c.  of 
concentrated  hydrochloric  acid  was  poured  into  the  funnel,  F, 
and  allowed  to  run  slowly  into  the  distilling  flask,  D,  through  the 
stop-cock,  S,  in  order  to  drive  off  the  air  in  the  lower  part  of  the 
stem  of  the  funnel,  which  would  disturb  the  regularity  of  the  acid- 
feed.  The  stop-cock  was  closed  and  the  funnel  filled  with  80  c.c. 
of  concentrated  hydrochloric  acid.  Now  heat  was  applied,  first 
with  a  smoky  flame,  and  when  the  solution  began  to  boil  was 
gradually  increased,  until  a  proper  flame  was  adjusted.  The 
hydrochloric  acid  in  the  funnel,  F,  was  now  allowed  to  run  into  the 
flask,  drop  by  drop,  at  such  a  rate  that  the  liquid  volume  in  the 
flask  might  be,  during  the  entire  distillation,  maintained  approxi- 
mately constant.  (The  rate  was,  usually,  about  three  drops  per 
two  seconds.)  When  the  acid  in  the  funnel,  F,  was  nearly 
exhausted,  the  distillation  was  complete.  The  receiver,  R,  con- 
taining the  distillate,  was  carefully  removed  and  then  the  flame 
was  turned  off.  The  content  in  the  distilling  flask  was  left  in 
place  to  cool  and  reserved  for  the  determination  of  antimony. 

The  distillate  was  transferred  into  a  no.  6  beaker  and  nearly 
neutralized  with  a  strong  (30  per  cent.)  solution  of  potassium 
hydroxide  and  the  neutralization  completed  with  a  saturated  solu- 


FIG.  i. 


14  ELECTRO-DEPOSITION  OF  COPPER  FROM 

tion  of  sodium  bicarbonate,  the  addition  of  an  excess  of  70  to 
80  c.c.  being  necessary.  The  neutralization  was  done  by  placing 
the  beaker  in  a  bath  of  cold  water,  in  order  to  keep  the  solution 
cool  while  the  neutralization  was  taking  place.  The  neutralized 
solution  was  then  titrated  with  a  standardized  solution  of  iodine 
(N/io).  Starch  solution  was  used  as  indicator. 

PRECAUTIONS  IN  THE  DISTILLATION  METHOD  OF  ARSENIC. 

The  analysis  of  arsenic  by  the  above  method  requires  careful 
manipulation.  In  order  to  do  it  successfully,  it  is  of  much  im- 
portance that  the  quantity  of  hypophosphorous  acid,  or  potassium 
hypophosphite,  added  for  the  reduction  should  be  limited  to  as 
small  amount,  as  given  in  the  above  procedure;  otherwise,  it  re- 
duces not  only  the  compounds  of  arsenic  and  antimony  to  their 
metallic  state,  but  also  those  of  other  metals,  such  as  iron,  copper, 
etc.  Over-reduction,  according  to  A.  E.  Knorr,9  would  fail  to 
give  satisfactory  results,  even  though  the  metallic  arsenic  and  anti- 
mony would  afterwards  re-dissolve  in  the  concentrated  hydro- 
chloric acid  solution.  It  is  also  important  that  complete  destruc- 
tion of  the  excess  of  hypophosphorous  acid,  or  potassium  hypo- 
phosphite,  should  be  accomplished  before  the  transference  of  the 
reduced  content  (solid  salts  and  solution)  into  the  distilling  flask 
takes  place.  Any  of  either  reducing  agents  remaining  unde- 
stroyed  will  interfere  with  the  determination,  and  the  result  will 
in  all  cases  be  low. 

The  advantages  of  having  a  continuous  acid-feed,  during  the 
entire  distillation,  are  great  and  manifold.  In  the  first  place,  the 
temperature  may  be  properly  regulated,  secondly,  the  strength  of 
the  hydrochloric  acid  in  the  distilling  flask  may  be  maintained  to 
prevent  the  reversible  action,  which  may  be  shown  by  the  follow- 
ing chemical  equation : 

As2O3  plus  6HC1  ±5  2AsCl3  plus  3H2O. 

and,  finally,  a  more  rapid  and  effective  distillation  may  result  and, 
therefore,  much  time  may  be  saved. 

In  order  to  secure  a  steady  flow  of  the  acid-feed,  a  grooved 
rectangular  board  of  asbestos,  E,  is  placed  on  the  mouth  of  the 
9  Private  communication. 


ELECTROLYTES  CONTAINING  ARSENIC.  i  5 

distilling  flask,  so  as  to  prevent  the  heating  of  the  stop-cock, 
which  would,  otherwise,  cause  irregularity  of  the  flow.  Back- 
suction  is  the  chief  cause  of  failure.  It  is  caused  either  by 
draught  or  by  variation  in  the  flame,  which  supplies  insufficient 
heat.  To  prevent  the  former  it  becomes  necessary  to  protect  the 
flame  from  draught  by  suspending  under  the  ring,  A,  an  asbestos 
cylinder,  P,  4^  inches  high  and  of  the  same  diameter  of  the  ring 
(see  Fig.  i).  To  prevent  the  latter,  the  flame  should  be  carefully 
regulated  from  time  to  time.  In  this  way,  back-suction  is  less 
liable  to  occur  and  success  may  be  insured.  If  the  distillate  is 
once  sucked  into  the  flask,  re-distillation  proves  absolutely  fruit- 
less, because  arsenous  chloride  refuses  to  distill  in  such  dilute 
solution. 

TEST  OF  THE  ABOVE  METHODS. 

The  accuracy  of  the  above  method  was  tested  according  to  the 
following  procedure:  A  weighed  sample  of  about  o.i  gm.  of  c.p. 
arsenous  oxide  was  dissolved  in  10  c.c.  of  sodium  hydroxide. 
When  the  solution  was  complete  50  c.c.  of  concentrated  nitric  acid 
was  added  and  then  20  c.c.  of  saturated  bromine  water,  in  order  to 
oxidize  the  arsenic  to  the  higher  state.  The  solution,  after  an 
addition  of  about  i  gm.  of  ferrous  sulphate,  was  heated  to  expel 
the  excess  of  bromine,  and,  after  adding  15  gm.  cupric  sulphate 
to  the  solution,  it  was  diluted  to  about  300  c.c.  and  heated  to 
boiling.  The  iron  and  arsenic  was  precipitated  with  concentrated 
ammonium  hydroxide  and  the  red  precipitate  was  treated  in  the 
same  way  as  above  described  (page  n). 

In  testing  this  method,  both  potassium  hypophosphite  and  hypo- 
phosphorous  acid  were  employed  as  reducing  agents.  In  the  case 
in  which  potassium  hypophosphite  was  used,  the  amounts  of 
arsenous  oxide  taken  for  analysis  were  0.1004  gm.  and  0.1014 
gm.,  which  corresponded  to  0.076  gm.  and  0.077  gm-  of  arsenic 
respectively,  and  the  analyses  gave  0.070  gm.  and  0.072  gm.  of 
arsenic.  In  the  case  where  hypophosphorous  acid  was  used,  the 
amounts  of  arsenous  oxide  were  0.1027  gm.  and  0.1014  gm.  which 
corresponded  to  0.078  gm.  and  0.077  gm-  arsenic  while  the 
analyses  gave  0.070  gm.  and  0.071  gm.  of  arsenic.  The  values  in 
both  cases  approximated  the  calculated  values  of  arsenic. 


1 6  ELECTRO-DEPOSITION  OF  COPPER  FROM 

REDUCING  AGENTS,  OTHER  THAN  HYPOPHOSPHOROUS  ACID  AND 
POTASSIUM  HYPOPHOSPHITE. 

As  has  already  been  said,  many  other  methods  of  treating  the 
iron  precipitate,  and  in  the  use  of  various  .reducing  agents,  were 
employed  for  the  distillation,  but  they  were  in  no  case  satis- 
factory. Of  these  methods  the  first  that  may  be  mentioned,  was 
that  which  practically  got  rid  of  all  the  copper  in  the  ferric 
hydroxide  precipitate,  first,  by  dissolving  the  iron  precipitate  with 
50  c.c.  of  hot  dilute  solution  of  hydrochloric  acid  (i  acid  to  5 
water)  through  the  filter,  and  precipitating  it  with  concentrated 
NH4OH  while  hot.  The  re-precipitated  precipitate  was  dissolved 
with  20  c.c.  of  concentrated  hydrochloric  acid  through  the  filter, 
and  filter  paper  was  washed  with  the  same  amount  and  kind  of 
acid.  This  was  then  transferred  into  the  distilling  flask  which 
had  previously  contained  15  grams  of  ferrous  sulphate,  and  dis- 
tillation was  made  according  to  the  method  given  by  E.  H.  Miller,10 
which  consisted  of  three  intermittent  distillations,  using  50  c.c. 
concentrated  hydrochloric  acid  each  time.  The  results  obtained 
varied  and  were  always  low  and  showed  that  ferrous  sulphate  did 
not  appear  in  this  case  to  be  a  satisfactory  reducing  agent.  Be- 
sides, the  distillation,  with  ferrous  sulphate  as  reducing  agent,  was 
difficult  to  control,  because,  as  the  solution  became  concentrated, 
it  often  happened  that  violent  bumping  was  inevitable,  sometimes 
so  violent  as  to  cause  the  distilling  flask  to  crack. 

The  combined  reducing  agents,  composed  of  stannous  chloride 
and  ferrous  sulphate,  were  next  employed,  and  the  object  of  using 
the  former  salt  was  to  decrease  the  amount  of  the  latter.  The 
solution  containing  iron,  arsenic  and  antimony  was  first  reduced 
by  adding,  drop  by  drop,  a  saturated  solution  of  stannous  chloride 
in  concentrated  hydrochloric  acid  until  it  became  colorless,  and 
then  transferred  into  the  distilling  flask  containing  7  grams  of  fer- 
rous sulphate  crystals.  The  distillation  was  made  as  before. 
But  this  also  proved  unsatisfactory  in  that  the  results  were  low, 
varying  from  15  per  cent,  to  even  50  per  cent. 

The  unsatisfactory  results  in  this  case  were,  perhaps,  due  to  the 
excess  and  strong  action  of  stannous  chloride,  which  caused  over- 

' "  Quantitative  Analysis  for  Mining  Engineers,"  E.  H.  Miller,  ed.  1904, 
p.  no. 


ELECTROLYTES  CONTAINING  ARSENIC.  17 

reduction  of  the  compounds  to  their  metallic  state  and  these  re- 
duced metals  remained  undissolved  even  in  a  concentrated  solu- 
tion of  hydrochloric  acid,  as  black  particles  were  observed  in  the 
flask  during  and  after  the  distillation.  Another  objection  to  the 
use  of  stannous  chloride  was  that  it  complicated  the  determina- 
tion of  antimony.  A.  E.  Knorr11  thinks  that  stannous  chloride  is 
not  a  good  reducing  agent  to  use  for  the  determination  of  arsenic, 
because  of  the  volatility  of  chloride  of  tin. 

Both  sodium  thiosulphate  and  ferrous  sulphate  were  also  tried, 
singly  and  combined.  The  iron  precipitate  with  the  filter  paper, 
in  this  case,  was  treated  with  20  c.c.  of  concentrated  nitric  acid  in 
a  350  c.c.  casserole  covered  with  watch-glass.  It  was  digested 
and  evaporated  on  a  hot  plate  untill  it  became  a  pasty  mass. 
After  addition  of  3  grams  of  potassium  bisulphate  (KHSO4) 
and  10  c.c.  of  concentrated  sulphuric  acid,  it  was  carefully  heated 
over  a  free  flame  until  fume  of  sulphuric  anhydride  was  strongly 
given  off.  The  solid  mass,  after  being  cooled,  was  taken  up  with 
30  c.c.  of  concentrated  hydrochloric  acid  and  distilled  as  before, 
using  either  i  gram  of  sodium  thiosulphate,  or  a  mixture  of  0.7 
gram  of  sodium  thiosulphate  and  7  grams  of  ferrous  sulphate 
crystals.  The  low  result  obtained  by  this  method  might  be  due 
partly  to  the  loss  of  solution  by  spattering  during  evaporation  to 
dryness  and  partly  to  the  interference  of  the  sulphur  dioxide 
which  was  liberated  by  the  decomposition  of  the  sodium  thio- 
sulphate. A  saturated  solution  of  sodium  thiosulphate,  instead 
of  solid  sodium  thiosulphate,  was  also  tried  and  the  reduced  solu- 
tion in  the  distilling  flask  was  boiled  for  a  few  minutes  before 
addition  of  the  hydrochlorous  acid,  in  order  to  expel  any  sulphur 
dioxide  that  might  be  present.  But  this  procedure  also  failed 
to  give  satisfactory  results,  they  being  low,  and  varying  from  20 
per  cent,  to  60  per  cent. 

DETERMINATION  OF  ANTIMONY. 

For  the  determination  of  antimony  Miller's12  method  was 
adopted.  After  the  separation  of  arsenic  by  distillation,  the  con- 
tent in  the  distilling  flask  was  transferred  into  a  no.  5  beaker  and 
diluted  to  about  400  c.c.  The  antimony,  together  with  the  copper, 

11  Private  communication. 

^"Quantitative  Analysis  for  Mining  Engineers,"  Miller,  1904,  p.  106. 


1 8  ELECTRO-DEPOSITION  OF  COPPER  FROM 

was  precipitated  in  warm  solution  with  a  stream  of  hydrogen 
sulphide  which  continued  to  pass  until  the  precipitate  settled  down 
and  the  solution  became  clear.  The  precipitate  was  separated 
first  by  decantation  and  then  by  filtration,  and  washed  three  times 
with  hydrogen-sulphide  water.  It  was  placed  with  the  filter  paper 
in  a  no.  2  beaker  and  treated  for  an  hour  at  room  temperature, 
with  50  c.c.  of  potassium  sulphide  (10  per  cent.)  solution.  The 
copper  sulphide  was  filtered  off,  washed  three  or  four  times  with 
hydrogen-sulphide  water  and  discarded.  To  the  filtrate  now  con- 
tained in  a  no.  5  beaker,  50  c.c.  of  dilute  sulphuric  acid  (i  acid 
to  4  water)  was  added  to  precipitate  the  antimony.  The  yellow 
precipitate  was  filtered  off  and  washed  with  hydrogen-sulphide 
water  three  times. 

The  antimony  sulphide,  together  with  the  filter  paper,  was 
placed  in  no.  2  beaker,  treated  with  40  c.c.  of  concentrated  hydro- 
chloric acid  and  oxidized  to  the  pentad  state  by  adding,  little  by 
little,  about  one  gram  of  potassium  chlorate,  and  the  solution  was 
heated  to  expel  the  free  chlorine.  (During  the  heating,  should 
the  solution  show  a  dark  coloration,  more  potassium  chloride 
should  be  added.) 

After  oxidation  and  the  complete  solution  of  the  antimony 
sulphide,  the  filter  paper  was  filtered  off  and  washed  three  or 
four  times  with  a  hot  dilute  solution  by  hydrochloric  acid  (i  part 
acid  to  3  parts  water).  The  filtrate  was  evaporated  to  50  c.c. 
so  as  to  make  the  solution  to  contain  a  constant  quantity  of 
hydrochloric  acid.  Twenty  c.c.  of  concentrated  hydrochloric  acid 
was  added  and  the  solution  diluted  from  600  to  700  c.c.  After 
the  addition  of  3  grams  of  potassium  iodide  crystals,  the  solution 
was  thoroughly  stirred  until  the  potassium  iodide  completely  dis- 
solved. It  was  then  titrated  at  room  temperature  with  a 
standardized  (N/io)  solution  of  sodium  thiosulphate,  starch  solu- 
tion being  used  as  indicator. 

As  the  liberation  of  all  iodine  does  not  take  place  instantane- 
ously it  is,  therefore,  necessary  to  titrate  the  solution  slowly,  that 
is,  the  thiosulphate  solution  should  be  run  into  the  solution  drop 
by  drop  until  the  blue  color  disappeared  at  least  for  one  minute. 
Should,  in  any  case,  the  blue  color  return,  immediately  more 
thiosulphate  solution  should  be  added. 


ELECTROLYTES  CONTAINING  ARSENIC.  19 

PREPARATION  OF  ELECTOLYTES. 

Two  standard  electrolytes  were  prepared  for  the  electrolyses. 

I.  Electrolyte  A,  which  contained  15  per  cent.  CuSO4-5H2O 
and  10  per  cent.  H2SO4,  by  weight. 

2,.  Electrolyte  B,  which  contained  15  per  cent.  CuSO4-5H2O, 
10  per  cent.  H2SO4  and  10  per  cent.  As  in  the  form  of  H3AsO4, 
by  weight. 

For  making  electrolyte  A,  160  grams  of  technical  bluestone 
crystals  from  Eimer  and  Amend,  New  York,  were  weighed  out 
and  dissolved  in  about  700  c.c.  of  water.  When  solution  was 
complete,  63  c.c.  of  concentrated  sulphuric  acid  (100  grams 
H2SO4)  were  added  to  it,  and  the  solution,  when  cooled,  was 
diluted  to  exactly  1,000  c.c.  The  electrolyte  was  analyzed  for 
copper  and  free  sulphuric  acid  according  to  the  following:  For 
the  copper  determination,  10  c.c.  of  the  electrolyte  was  drawn  out 
by  means  of  a  pipette,  transferred  into  a  250  c.c.  calibrated  flask 
and  diluted  to  that  volume.  After  stirring  thoroughly,  50  c.c. 
of  it  was  taken  and  diluted  to  100  c.c.  and  concentrated 
ammonium  hydroxide  added  in  slight  excess.  The  solution  was 
boiled  in  order  to  expel  the  excess  of  ammonia,  and  then  acetic 
acid  added  in  slight  excess.  The  solution  was  allowed  to  cool  to 
ordinary  temperature  and  titrated  after  an  addition  of  3  grams 
of  potassium  iodide  with  a  standardized  solution  of  sodium  thio- 
sulphate,  starch  solution  being  used  as  indicator.  Two  analyses 
gave  3.822  per  cent,  and  3.824  per  cent,  of  copper,  the  average  of 
which  corresponded  to  15.01  grams  of  CuSO4-5H2O  per  100  c.c. 
of  solution. 

The  method  used  for  analyzing  the  free  sulphuric  acid  in  the 
electrolyte  consisted  in  determining  the  total  sulphate.  This  was 
conducted  as  follows :  50  c.c.  of  the  above  diluted  solution  was 
measured  out  and  diluted  to  about  300  c.c.  After  an  addition  of 
a  few  drops  of  hydrochloric  acid,  the  solution  was  brought  to 
boiling,  and  50  c.c.  of  barium  chloride  (20  grams  BaCl2  in  1,000 
c.c.)  was  slowly  added  with  constant  stirring.  When  the  barium 
sulphate  settled  down,  it  was  filtered  by  decantation  and  washed 
with  hot  water  three  times.  The  precipitate  was  ignited  in  a 
porcelain  crucible  and  weighed.  The  difference  between  the  total 
sulphate  and  the  sulphate  as  copper  sulphate  is  the  free  sulphuric 


2O  ELECTRO-DEPOSITION  OF  COPPER  FROM 

acid.  The  electrolyte  was  found,  by  this  method,  to  contain  9.92 
grams  of  free  sulphuric  acid  per  100  c.c.  solution. 

The  preparation  of  electrolyte  B,  consisted  in  dissolving  100 
grams  of  metallic  arsenic  in  a  sufficient  quantity  of  concentrated 
nitric  acid  in  a  no.  5  beaker,  much  excess  being  avoided.  After 
complete  dissolution  of  arsenic,  63  c.c.  of  sulphuric  acid  was 
added  and  the  solution  was  heated  on  a  hot  plate  until  the  arsenic 
acid  separated  out  and  became  a  white  pasty  mass,  which  indi- 
cated complete  expulsion  of  nitric  acid.  The  arsenic  acid  was 
taken  up  with  200  to  300  c.c.  of  water;  at  the  same  time  160 
grams  of  technical  bluestone  crystals  were  dissolved  in  about  300 
c.c.  of  water,  in  another  beaker.  The  two  solutions  were  mixed 
and  diluted  exactly  to  1,000  c.c.  The  arsenic  in  this  electrolyte 
was  determined  as  follows :  10  c.c.  of  the  electrolyte  was  measured 
out  and  diluted  exactly  to  500  c.c.  in  a  calibrated  flask,  from 
which  50  c.c.  was  drawn  for  analysis.  It  was  evaporated  to  sul- 
phuric fume  with  an  addition  of  8  c.c.  of  concentrated  sulphuric 
acid.  The  reduction,  distillation  and  titration  were  conducted  in 
the  same  way  as  in  the  case  of  determining  arsenic  in  cathode 
copper.  The  analyses  showed  that  the  electrolyte  contained  10.01 
and  9.91  grams  arsenic  in  100  c.c.  of  solution. 

The  electrolytes  used  for  electrolysis  were  made  to  contain 
1.5  per  cent.,  2  per  cent.,  3  per  cent.,  4  per  cent.,  6  per  cent.,  and 
8  per  cent.,  of  arsenic  prepared  from  the  above  two  standard 
electrolytes,  by  mixing  as  follows : 

(a)  For  electrolyte  containing  1.5  per  cent,  arsenic,  10  per  cent, 
free  H2SO4  and  15  per  cent.  CuSO4-5H2O,  850  c.c.  of  electrolyte 
A  was  mixed  with  150  c.c.  of  electrolyte  B. 

(b)  For  electrolyte  containing  2  per  cent,  arsenic,  10  per  cent, 
free  H2SO4  and  15  per  cent.  CuSO4-5H2O,  800  c.c.  of  electrolyte 
A  was  mixed  with  200  c.c.  of  electrolyte  B. 

(c)  For  electrolyte  containing  3  per  cent,  arsenic,  10  per  cent, 
free  H2SO4  and  15  per  cent.  CuSO4-5H,O,  700  c.c.  of  electrolyte 
A  was  mixed  with  300  c.c.  of  electrolyte  B. 

(d)  For  electrolyte  containing  4  per  cent,  arsenic,  10  per  cent, 
free  H2SO4  and  15  per  cent.  CuSO4-5H2O,  600  c.c.  of  electrolyte 
A  was  mixed  with  400  c.  c.  of  electrolyte  B. 

(e)  For  electrolyte  containing  6  per  cent,  arsenic,  10  per  cent, 
free  H2SO4  and  15  per  cent.  CuSO4-5H2O,  400  c.c.  of  electrolyte 
A  was  mixed  with  600  c.c.  of  electrolyte  B. 


ELECTROLYTES  CONTAINING  ARSENIC.  21 

(/)  For  electrolyte  containing  8  per  cent,  arsenic,  10  per  cent, 
free  H2SO4  and  15  per  cent.  CuSO4-5H2O,  200  c.c.  of  electrolyte 
A  was  mixed  with  800  c.c.  of  electrolyte  B. 

THE  ELECTROLYSIS. 

The  electrolyses  were  conducted  in  no.  6  beakers  (size  4^  inches 
in  diam.  and  5f  inches  high)  in  each  of  which  was  immersed  an 
anode  and  a  cathode  (size  4§  inches  long  and  2j  inches  wide),  the 
latter  being  plates  cut  from  sheet  copper,  %4  inch  thick.  The  anodes 
were  cast  plates  of  copper  f  inch  thick.  Before  the  cathodes  were 
used  they  were  straightened  and  cleaned  by  washing  first  with  a 
little  dilute  nitric  acid  and  then  with  water,  which  gave  a  clean 
bright  surface.  A  horizontal  mark  was  made  on  each,  4  inches 
from  the  bottom,  so  as  to  obtain  the  desired  current  density,  and 
the  surfaces  were  greased  with  a  little  vaseline.  The  anode  and 
the  cathode  in  each  cell  were  suspended  from  glass  rods  (e,  Fig.  2) 
at  a  distance  of  if  inch  and  parallel  to  each  other.  The  current 
density  used  in  all  experiments  was  40  amperes  per  square  foot. 

THE  APPARATUS. 

The  apparatus  and  its  arrangement  are  shown  in  Fig.  2.  This 
consists  of  two  water-baths  (W)  which  are  used  to  keep  the 
electrolyte  at  constant  temperatures  and  in  each  of  which  were 
placed  four  cells  (C)  (no.  6  beakers).  Each  cell  rests  on  two 
strips  of  wood,  s,  and  the  water-baths  are  supported  at  each  end 
by  an  iron  tripod  (/).  Under,  and  in  the  middle  of  each  water- 
bath  is  placed  a  Bunsen  burner  (B)  by  which  the  desired  tem- 
peratures of  the  two  baths  may  be  secured  and  adjusted.  All  the 
cells  are  connected  in  series.  The  electric  current  used  for  elec- 
trolysis is  furnished  by  a  storage  battery  of  six  cells,  connected  in 
series,  measured  by  the  ammeter  (A),  which  permits  readings  to 
0.05  ampere,  and  regulated  by  the  rheostat  (R). 

CIRCULATION  OF  ELECTROLYTE. 

The  electrolyte  in  each  cell  was  agitated  during  electrolysis  by 
stirrer  (g).  Fig.  2  shows  its  arrangement  and  details.  It  con- 


22 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


sists  of  the  framework  of  which  (F)  are  the  two  horizontal  steel 
bars,  and  the  ends  of  which  are  clamped  to,  and  supported  by  a 
vertical  iron  rod  (L).  To  each  of  the  steel  bars  (F)  are  clamped 
four  cylindrical  collars  (h),  at  such  distance  as  to  conveniently 
permit  the  stirrers  to  operate  in  the  cells.  The  pulleys  (p)  ( J  inch 
diam.),  fastened  to  the  stirring  rods  (/),  rest  on  the  collars  (h). 
The  upper  part  of  the  stirring  rod  (/)  is  of  steel  and  the  lower 


fi/W    VIE*/   Of    CCLt-3 


FIG.  2. 


part  (g)  of  glass  rod,  and  these  two  parts  are  connected  by  means 
of  a  short  piece  of  rubber  tubing  (r).  Two  "policemen"  (b) 
attached  to  the  glass  rod,  as  are  shown  in  Fig.  2,  serve  to  give 
an  effective  circulation  of  the  electrolyte  in  each  cell.  The  stirrers 
are  run  by  a  half  horse-power  motor  (M).  The  speed  of  the 
stirrers  is  about  120  revolutions  per  minute. 


ELECTRO-DEPOSITION  OF  COPPER  FROM  23 

MODE  OF  OPERATION. 

In  these  experiments  the  mode  of  operation  is  simple  and  may 
be  stated  as  follows :  After  all  the  connections  of  the  circuit  had 
been  made,  and  the  electrodes  had  been  properly  placed  and  ad- 
justed, the  cells  were  filled  with  electrolyte  until  its  surface 
reached  the  horizontal  mark  of  the  cathodes,  which,  as  has  already 
been  said,  were  scratched  for  the  purpose  of  obtaining  the 
desired  current  density  and  which  also  served  to  keep  the  volume 
of  the  electrolyte  constant.  Water  was  then  run  into  the  two 
baths  (W)  until  they  became  full.  The  stirrers  were  set  in 
motion,  and  the  baths  (W)  heated.  When  the  desired  tempera- 
tures of  the  electrolytes  were  attained,  the  electric  current  for 
electrolysis  was  turned  on  and  kept  constant  by  regulating  the 
rheostat  (R).  The  difference  of  potential  between  the  anode  and 
the  cathode  was  read  every  two  hours  and  sometimes  every  three 
hours  with  a  voltmeter  which  permits  reading  to  o.oi  of  a  volt. 
The  temperatures  of  the  electrolyte  were  measured  with  thermo- 
meters (T)  immersed  in  the  cells.  At  the  end  of  the  experiment 
the  glass  part  of  the  stirrers  was  disconnected.  The  cathode 
copper  was  removed  from  the  cells,  washed  and  dried. 

During  electrolysis,  it  was  observed  that  much  water  of  the 
electrolyte  was  lost  by  evaporation.  To  make  up  this  loss,  water 
was  added  to  the  cells  from  time  to  time. 

SAMPLE  OF  CATHODE  COPPER  FOR  ANALYSIS. 

In  order  to  easily  peel  off  the  starting  sheet,  the  edges  of  the 
cathode  were  first  sawed  off,  and  the  deposited  copper  was  sawed 
into  strips  from  -J  to  f  inch  wide,  and  from  3  to  3^  inches  long. 
These  strips  were  used  as  samples  for  analysis,  usually  about  80 
grams,  unless  the  copper  deposit  shows  dark  surface  and  is 
brittle,  indicating  much  impurities,  in  the  latter  case  a  sample  of 
40  grams  was  taken. 

ELECTROLYTES,  WHICH  CONTAINED  NO  ADDITION-AGENT. 
Experiment  I. 

Four  runs  were  made  on  electrolytes  which  contained  no 
"  addition-agent."  Electrolytes  used  for  Experiment  I.  contained 


24 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


15  per  cent,  cupric  sulphate  (CuSO4-5H2O),  10  per  cent,  sul- 
phuric acid:  and  cell  i,  no  arsenic;  cell  2,  i  per  cent,  arsenic; 
cell  3,  2  per  cent,  arsenic ;  and  cell  4,  4  per  cent,  arsenic.  The 
electrolysis  was  conducted  for  53  hours,  in  two  series,  each  of 
which  consisted  of  four  cells,  C,  as  is  shown  in  Fig.  2.  The  com- 
position of  the  electrolytes  in  the  two  series  was  the  same,  but 
the  temperature  of  the  electrolyte  was  20°  C.  and  50°  C. 

It  was  observed  during  electrolysis,  that  the  potential  difference 
between  ithe  electrodes  in  the  lower-temperature  series  was 
gradually  increased  and  that  in  the  higher-temperature  one  only 


to  a  small  extent,  and  sometimes  remained  practically  constant. 
The  increase  of  voltage  was  due  to  the  fact  that  a  sticky  coating 
of  oxides  of  arsenic  and  antimony  gradually  formed  on  the  sur- 
face of  the  anode.  But  the  coating  'formed  at  a  higher  temper- 
ature was  porous  and  offered  little,  or  no,  resistance  and  dropped 
to  the  bottom  of  the  cell  when  sufficiently  thick.  In  order  to 
prevent  the  accumulation  of  the  coating  on  the  anodes  in  the 
lower-temperature  series,  the  surfaces  were  occasionally  scraped.. 


ELECTROLYTES  CONTAINING  ARSENIC. 


It  may  be  here  mentioned  that  this  experiment  was  attempted  to 
run  continuously,  in  other  words,  day  and  night ;  but  it  was  soon 
realized  that  this  could  not  be  done,  because  two  of  the  conditions 
could  not  be  properly  maintained  during  the  night.  In  the  first 
place,  the  coating  of  arsenic  and  antimony  oxides  which  formed 
on  the  surface  of  the  anodes  in  the  lower-temperature  series  was 
so  thick  that  it  greatly  increased  the  resistance,  thus  reducing  the 
current  density :  and  in  the  second  place,  the  addition  of  water  to 
the  electrolytes  to  make  up  the  loss  by  evaporation  could  not  be 
readily  accomplished.  The  result  was  that  the  hotter  electrolytes 
became  greatly  concentrated.  As  the  deviations  of  these  condi- 
tions might  have  exerted  a  strong  influence  upon  the  physical  and 
chemical  properties  of  the  deposit,  analyses  of  the  cathode  copper 
for  arsenic  and  antimony  were  not  made,  nor  were  these  two 
elements  determined  in  the  electrolyte  after  the  run. 

In  regard  to  the  character  of  the  deposits,  a  few  words,  however, 
may  be  said.  It  was  observed  that  the  deposits  formed  at  50°  C. 
were,  by  far,  better  than  those  formed  at  20°  C.  They  were  solid, 
coherent,  and  of  bright  color,  though  nodular  crystals  formed  at  the 
lower  edge,  especially  in  electrolytes  containing  higher  percentage 
of  arsenic.  The  deposits  which  formed  at  20°  C.  in  electrolytes 
containing  I  per  cent.,  2  per  cent.,  and  4  per  cent.,  were  dark, 
brittle,  and  crystalline,  and  the  crystals  were  easily  broken  off. 
The  deposit  formed  at  20°  C.  in  electrolyte  which  originally  con- 

TABLE  I. 

Time  of  Experiment  53  hours.  Current  Density  40  Amp.  per  square 
foot.  Distance  between  Electrodes  1.75  inch.  Electrolyte  contained  15 
per  cent.  CuSO.i-5H2O  and  10  per  cent.  H2SO4.  Anode  contained  1.15  per 
cent.  As  and  1.05  per  cent  Sb. 


No.  of  Cells. 

Per  Cent,  of  As  in 

Electrolyte. 

Temp,  of  Electrolyte 
deg.  Cent. 

Photo.  I. 

Series  A. 

A 

i 

O.O 

20 

i 

2 

2.0 

2O 

2 

3 

4.0 

20 

3 

4 

4.0 

20 

4 

Series  B. 

B 

i 

O.O 

50 

i 

2 

I.O 

50 

2 

3 

2.O 

50 

3 

4 

4.0 

50 

d 

26 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


tained  no  arsenic,  appeared  bright.  The  deposits  are  shown  in 
Photograph  I.  The  upper  row  (A)  are  deposits  formed  at  20°  C. 
and  the  lower  row  (B)  are  deposits  formed  at  50°  C. 


Experiment  II. 

This  experiment  was  conducted  in  the  same  manner  as  the 
previous  one,  except  that  the  electrolysis  was  carried  on  only 
during  the  day-time.  The  electrolytes  used  for  this  experiment 
contained  2  per  cent.,  4  per  cent.,  6  per  cent.,  and  8  per  cent,  of 
arsenic  with  the  usual  proportion  of  cupric  sulphate  (15  per  cent. 
CuSO4-5H2O)  and  free  sulphuric  acid  (10  per  cent.  H2SO4). 


The  temperatures  of  the  two  series  were  35°  C.  and  60°  C.,  and 
the  time  of  the  experiment  was  42  hours. 

The  deposits  formed  at  35°  C.  and  in  electrolytes  containing 
2  per  cent.,  4  per  cent.,  and  6  per  cent,  arsenic  were  bad  and 
brittle  and  composed  of  coarse  grains  which  were  easily  detached. 
Their  surfaces  became  dark  as  soon  as  they  were  taken  out  of  the 


ELECTROLYTES  CONTAINING  ARSENIC.  27 

electrolytes  and  exposed  to  the  air.  The  analysis  shows  that 
these  deposits  were  high  in  arsenic  and  antimony  (see  no.  I,  2,  and 
3,  Table  II.).  The  deposit  formed  in  electrolyte  containing  8  per 
cent,  arsenic  and  at  the  same  temperature  (35°  C.)  was  much 
better.  It  was  good,  bright,  and  coherent,  and  ran  low  in  arsenic 
and  antimony  (see  no.  4,  series  A,  Table  II. ).  But  it  was 
observed  that  at  the  edges  of  this  deposit  dendritic  nodules 
formed,  and  smaller  nodules  were  scattered  over  the  surface. 
This  is  clearly  shown  in  series  A,  Photograph  II.  The  deposits 
formed  at  60°  C.  and  in  electrolytes  which  contained  2  per  cent, 
and  4  per  cent,  arsenic  were  also  bad,  brittle,  crystalline  and  in- 
coherent. "  Trees  "  were  formed  at  the  edges  as  shown  in  I  and 
2,  series  B,  Photograph  II.  Their  surfaces  were  dark  and  became 
darker  when  exposed  to  air.  They  ran  much  higher  in  arsenic 
and  antimony  than  those  formed  at  the  lower  temperature  and 
in  similar  electrolytes.  Those  formed  at  60°  C.  but  in  electro- 
lytes containing  6  per  cent,  and  8  per  cent,  arsenic  were,  on  the 
other  hand,  good,  bright,  solid  and  coherent,  though  larger 
"  trees  "  were  found  at  the  edges,  especially  of  the  deposit  formed 
in  electrolytes  containing  8  per  cent,  arsenic.  3  and  4,  series  B, 
Photograph  II.,  show  the  "  trees  "  of  these  deposits. 

The  analysis  of  the  electrolytes  after  the  run,  as  given  in  Table 
II.,  shows  that  they  contained  higher  percentage  of  arsenic  than 
before  the  run.  This  increase  was,  undoubtedly,  due  to  the 
partial  dissolution  of  the  arsenic  in  the  anode.  The  antimony, 
both  in  the  cathode  copper  and  in  the  electrolyte  was  also  trans- 
ferred from  the  anode  by  the  current. 

The  potential  difference  between  the  electrodes  should  also  be 
mentioned.  It  was  observed  that  the  potential  difference  in  series 
A  was  higher  on  the  first  day  than  on  the  last  day  of  the  run,  while 
that  in  series  B  was  not  so  in  every  case.  The  potential  difference 
in  cells  I  and  2,  series  B,  was  higher  on  the  last  day  than  the  first 
day  of  the  run.  This  may  be  explained  by  the  fact  the  formation 
of  the  porous  layer  of  oxides  of  arsenic  and  antimony  on  the 
anode  which,  at  the  time  when  the  voltage  was  read,  did  not  drop 
off,  and,  therefore,  offered  resistance.  In  series  A  the  anodes 
were  scraped  occasionally  and  readings  were  taken  just  after 
scraping.  The  diminution  of  potential  difference  may  be  due  to 
the  formation  of  nodular  crystals,  reducing  the  actual  distance 
between  the  electrodes. 


28 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


TABLE  II. 

Time  of  Experiment  was  42  hours.  Distance  between  Electrodes  was 
1.75  inch.  Electrolytes  contained  15  per  cent.  CuSCX-sHcO  and  10  per  cent. 
H2SO4.  Anode  contained  1.15  per  cent.  As  and  1.05  per  cent.  Sb.  Current 
Density  was  40  Amp.  per  square  foot. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  deg.  Cent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
II. 

£  As. 

%  Sb. 

A.. 

4  Sb. 

Series  A. 

A 

i 

2 

35 

0.58 

0.199 

0.253 

2.22 

0.004 

I 

2 

4 

35 

0-57 

0.217 

0.391 

4-32 

O.OO2 

2 

3 

6 

35 

0-53 

0.314 

0.361 

6.15 

0.003 

3 

4 

8 

35 

0-59 

0.036 

O.OI4 

8.15 

O.O04 

4 

Series  B. 

B 

i 

2 

60 

0-45 

O.026 

0-395 

2.29 

O.OO6 

i 

2 

4 

60 

0.42 

0.388 

0.496 

n.d. 

n.d. 

2 

3 

6 

60 

0.39 

O.OlS 

0.009 

6.23 

O.OO2 

3 

4 

8 

60 

0.38 

O.OI4 

0.004 

8.10 

0.004 

4 

Experiment  III. 

In  this  experiment  the  cathodes  were  surrounded  with  dia- 
phragms, and  the  object  of  using  them  was  to  prevent  particles  of 
impurity  from  depositing  mechanically  on  the  cathode.  The 
diaphragm-frame  was  made  of  glass  rod  and  was  of  semi-cylin- 
drical shape  (D,  Fig.  2).  The  circular  side  and  the  bottom  of  the 
frame  were  closed  with  thin  rubber  dam,  used  by  dentists,  and  the 
side,  which  is  between  the  electrodes  with  linen  cloth.  The 
cloth,  before  used,  was  thoroughly  washed  with  hot  water,  and 
the  rubber  dam  was  first  treated  with  dilute  sulphuric  acid  and, 
then,  with  water,  in  order  to  free  any  impurity  that  might  have 
been  present. 

During  the  electrolysis  one  difficulty  was  encountered  when  the 
cathodes  were  surrounded  with  diaphragms.  The  latter,  when 
soaked  with  electrolyte  and  in  contact  with  the  former,  became 
cathodes,  and  thus  copper  was  deposited  on  their  sides  and  bottom, 
which  soon  bridged  the  electrodes  and  short-circuited  the  electric 
current.  Moreover,  rubber  dam  was  found  not  a  proper  ma- 
terial to  use  because  it  decayed  and  became  tender,  and,  because 
it  increased  the  potential  difference  between  the  electrodes  to  a 
small  extent. 

The  electrolysis  was  conducted  at  60°  C.  and  30°  C.  and  the 


ELECTROLYTES  CONTAINING  ARSENIC. 


29 


electrolytes  used  for  both  series  contained  2  per  cent,  and  6  per 
cent,  arsenic  with  the  same  proportion  of  cupric  sulphate  (15  per 
cent.)  and  free  sulphuric  acid  (10  per  cent.)  as  before. 

As  has  already  been  stated,  a  sticky  layer  of  oxides  formed 
on  the  surface  of  the  anode  in  the  low-temperature  series,  and 
the  formation  of  this  caused  the  potential  difference  between  the 
electrodes  to  be  unusually  high.  To  show  whether  or  not  this 
high  potential  difference  had  any  effect  on  the  deposition  of 
arsenic  and  antimony  on  the  cathode,  the  surface  of  two  anodes 
(nos.  i  and  3,  series  A,  Table  III.)  was  occasionally  scraped  with  a 
rubber  "  policeman  "  attached  to  a  glass  rod,  while  the  surface  of 
the  other  two  anodes  of  series  A  (nos.  2  and  4,  Table  III.)  was 
undisturbed. 

Table  III.  gives  the  results  of  this  experiment  and  shows  the 
averaged  potential  difference  is  much  higher  in  the  case  where 
the  anode  surface  was  not  scraped  than  that  in  the  case  where  the 
anode  surface  was  scraped.  The  amount  of  arsenic  in  the  de- 
posited copper  is  practically  the  same  in  both  cases,  while  the 
amount  of  antimony  appears  little  higher  in  the  case  where  the 
anode  surface  was  unscraped. 

As  to  the  physical  properties,  the  deposits  which  formed  at  30° 
C.  were  all  bad,  brittle  and  high  in  arsenic  and  antimony,  as  is 
shown  in  Table  III.,  and  composed  of  coarse,  nodular  and  in- 

TABLE  III. 

Time  of  Experiment  61  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSC-i-sHoO  and  10  per  cent.  H2SO4.  Anode  contained  1.15  per 
cent.  As  and  1.05  per  cent  Sb. 


No.  of 
Cells. 

Per  Cent. 

of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  deg.  Cent. 

Average 
E.M.F. 

in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 

III. 

^  As. 

0  Sb. 

4  As. 

*Sb. 

Series  A. 

A 

i 

2 

30 

0-57 

O.II8 

0.099 

2.40 

0.003 

i 

2 

2 

30 

0.79 

O.II5 

0.129 

2.  II 

None 

2 

3 

6 

30 

O.62 

O.I24 

0.053 

5-80 

0.003 

3 

4 

6 

30 

1.  12 

0.160 

0.079 

6.10 

0.002 

4 

Series  B. 

B 

i 

2 

60 

0.49 

0.186 

0.268 

2.28 

0.004 

i 

2 

2 

60 

0.44 

0.171 

0.228 

2.21 

O.OO2 

2 

3 

6 

60 

0.44 

0.025 

O.OOI 

6.28 

O.002 

3 

4 

6 

60 

0.46 

0.031 

O.OOI 

6.3O 

0.004 

4 

30  ELECTRO-DEPOSITION  OF  COPPER  FROM 

coherent  crystals.  The  deposits  which  formed  at  60°  C.  and  in 
the  electrolyte  containing  2  per  cent,  arsenic  were  very  bad. 
They  were  dark,  and  became  darker  when  exposed  to  the  air. 
The  analysis  shows  that  they  contained  much  arsenic  and  anti- 


mony.  Those,  on  the  other  hand,  which  formed  at  the  same 
temperature  but  in  electrolyte  containing  6  per  cent,  arsenic,  were 
good,  bright  and  dense,  though  a  few  nodular  crystals  formed  on 
the  surface  and  at  the  edges  of  the  deposits.  Photograph  III., 
63  and  I>4,  shows  their  character. 


Experiment  IV. 

In  this  experiment,  and  in  the  rest  of  the  experiments,  muslin 
diaphragms  were  used  to  surround  the  anodes,  instead  of  the 
cathodes.  These  diaphragms  were  found  satisfactory;  short- 
circuiting  was  prevented  and  particles  of  impurities  were  col- 
lected and,  thus,  prevented  from  collecting  mechanically  on  the 
cathode. 


ELECTROLYTES  CONTAINING  ARSENIC.  31 

The  electrolytes  used  were  prepared  to  contain  1.5  per  cent., 
3  per  cent.,  6  per  cent.,  and  8  per  cent,  arsenic,  and  the  amount 
of  cupric  sulphate  and  free  sulphuric  acid  was  15  per  cent,  and 
10  per  cent.,  respectively.  The  temperature  of  the  electrolytes 
was  40°  C.  and  50°  C.  and  the  time  of  electrolysis  was  104  hours. 
Table  IV.  gives  the  results  of  this  experiment. 

The  deposits,  no.  i,  no.  2  and  no.  3,  series  A,  were  all  bad. 
rough,  brittle,  and  crystalline.  Of  these  deposits,  no.  2  and  no.  3 


TABLE  IV. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSCX-sHoO  and  10  per  cent.  H2SO4.  Anode  contained  0.75  per 
cent.  As  and  0.73  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  cleg.  Cent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
IV. 

jTAs. 

5*Sb. 

$As. 

*Sb. 

Series  A. 

A 

i 

i-5 

40 

0.44 

0.077 

0.085 

1.72 

0.004 

i 

2 

3-0 

40 

0.44 

O.IOO 

0.074 

3-09 

0.004 

2 

3 

6.0 

40 

0.43 

O.IOI 

0.117 

6.03 

0.003 

3 

4 

8.0 

40 

0.49 

0.024 

0.005 

8.10 

0.005 

4 

Series  B. 

B 

i 

i-5 

50 

0.40 

0.063 

0.175 

1.65 

Not    de- 

i 

tectable. 

2 

3-0 

50 

0.40 

0.296 

0.460 

3-27 

0.004 

2 

3 

6.0 

50 

0.41 

0.007 

O.OOI 

6.10 

0.004 

3 

4 

8.0        1        50 

0.44 

0.008 

O.OO2 

8.04 

0.003 

4 

were  worse;  they  were  composed  of  crystals  easily  detached,  and 
consisted  of  long  dendritic  "  trees "  which  interfered  with  the 
operation  of  stirrers  and  tended  to  short-circuit  the  current. 
Their  surfaces  were  dull  and  became  dark  on  exposure  to  the 
atmosphere.  The  chemical  analyses  show  that  they  contain  much 
arsenic  and  antimony.  Deposit  no.  4,  series  A,  was  good,  solid, 
bright,  and  absent  of  "  trees,"  but  consisted  of  a  few  small  nodular 
crystals  which  scattered  over  the  surface.  It  contained  a  very 
small  amount  of  arsenic  and  antimony. 

The  deposits,  no.  i  and  no.  2,  series  B,  which  formed  at  50°  C. 
and  in  electrolytes  containing  1.5  per  cent,  and  3  per  cent,  arsenic, 
respectively,  were  also  bad  and  brittle,  and  both  were  composed 
of  Iqng  dendritic  "  trees."  It  was  observed  that  deposit  no.  2 


32  ELECTRO-DEPOSITION  OF  COPPER  FROM 

was  much  worse  than  no.  i,  as  it  was  very  brittle  and  dark.  The 
analysis  shows  that  both  deposits  contained  high  percentage  of 
arsenic  and  antimony,  but  the  percentage  of  these  two  impurities 
contained  in  deposit  no.  2  was  by  far  higher  than  that  in  deposit 
no.  i.  As  to  the  deposits  no.  3  and  no.  4,  series  B,  which  formed 
at  the  same  temperature  but  in  electrolytes  containing  6  per  cent. 


and  8  per  cent,  arsenic,  they  were  found  to  be  good,  solid,  bright 
and  absent  of  "  trees,"  though  a  few  rounded  nodules  formed  on 
the  surface.  They  contained  very  low  arsenic  and  antimony,  as 
shown  in  Table  IV.  Photograph  IV.  shows  the  character  of  the 
deposits. 

ELECTROLYTES,  WHICH  CONTAINED  INORGANIC  "ADDITION- 
AGENTS." 

This  series  of  experiments  was  conducted  with  electrolytes  of 
the  same  composition  as  those  used  in  Experiment  IV.,  with  the 
exception  that  inorganic  "  addition-agent "  was  added.  The 
temperature  of  electrolytes  in  series  A  was  40°  C.  and  that  in 
series  B  was  50°  C. 


ELECTROLYTES  CONTAINING  ARSENIC. 


33 


Experiment  V. 

In  this  experiment  sodium  chloride  was  used  as  "  addition- 
agent/'  0.1650  gram  of  this  salt  was  weighed  out  and  added  to 
a  liter  of  each  electrolyte,  in  other  words,  the  electrolytes  con- 
tained o.oi  per  cent,  chlorine  or  0.0065  Per  cent,  sodium  in  the 
form  of  sodium  chloride. 

It  may  be  pointed  out  here  that  when  sodium  chloride  was 
added  to  the  electrolyte  it  reacted  with  the  cupric  sulphate  to  form 
cupric  chloride  and  sodium  sulphate,  as  may  be  shown  by  the  fol- 
lowing equation. 

2NaCl  plus  CuSO4  =  CuCl2  plus  Na2SO4. 

Thus,  there  were  present  in  the  electrolyte,  in  fact,  two  "  addition- 
agents,"  instead  of  one,  when  sodium  chloride  was  added. 

The  results  of  this  experiment  were  very  satisfactory  and  are 
shown  in  Table  V. 

TABLE  V. 

Time  of  Experiment  was  104  hours.  Distance  between  Electrodes  was 
1.75  inch.  Current  Density  was  40  Amp.  per  square  foot.  Electrolytes 
contained  15  per  cent.  CuSOi-sHsO  and  10  per  cent.  HaSO*  and  o.oi  per 
cent.  Cl  as  NaCl.  Anode  contained  0.87  per  cent.  As  and  1.13  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  deg.  Cent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
V. 

$  As. 

jf  Sb. 

%  As. 

^Sb. 

Series  A. 

A 

i 

i-5 

40 

0.48 

O.OOI2 

0.0005 

1.97 

0.0056 

i 

2 

3-0 

40 

0.56 

O.OOO6 

0.0005 

3-39 

0.0036 

2 

3 

6.0 

40 

0.51 

O.OOI9 

0.0008 

6-59 

0.0056 

3 

4 

8.0 

40 

0-54 

O.OOI9 

O.OOO7 

8-51 

0.0098 

4 

Series  B. 

B 

i 

1-5 

50 

0.47 

O.OO24 

0.0003 

1-90 

0.0036 

i 

2 

3-0 

50 

0.49 

O.OOI2 

0.0005 

3-43 

0.0097 

2 

3 

6.0 

50 

0.47 

O.OOI2 

0.0005 

6.70 

0.0090 

3 

4 

8.0 

50 

0.49 

O.OOO6 

0.0004 

8.60 

0.0058 

4 

The  deposits  from  series  A  were  very  good,  bright,  solid, 
smooth,  coherent  and  absolutely  absent  of  "  trees."  The  deposits 
from  series  B  were  similar  to  those  from  A,  except  that  their 
surfaces  were  little  brighter  and  the  small  crystals  were  a  bit  more 
pronounced.  The  analyses  of  these  deposits  show  that  the 
arsenic  and  antimony  were  very  low  in  every  case. 

In  addition  to  the  chemical  determination  of  the  impurities  in 


34 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


the  cathode  copper,  a  physical  bending  test  was  also  made.  A 
strip  of  the  cathode  copper,  about  f  inch  wide,  3}  inches  long,  was 
taken  for  the  test.  It  was  bent,  with  the  under-side  out  and  ham- 
mered double ;  in  no  case  did  the  strips  crack  at  the  bend.  This 
bending  test  showed  that  the  cathode  copper  was  very  ductile 
and  of  high  purity  in  all  cases. 

The  addition  of  such  a  small  amount  of  sodium  chloride  was 
found  to  exert  a  remarkably  favorable  influence  upon  the  deposited 


V 


copper,  for  it  not  only  improved  the  physical  properties  of  the 
deposits,  but  also  overcame  the  formation  of  "  sprouts,"  and  pre- 
vented the  precipitation  of  arsenic  and  antimony  with  the  cathode 
copper.  (Compare  results  given  in  Tables  IV.  and  V.)  Photo- 
graph V.  shows  the  character  of  the  deposits. 

Experiment  VI. 

As  has  been  found,  that  the  presence  of  a  small  amount  of 
sodium  chloride  in  the  electrolvtes  exerts  a  marked  beneficial  in- 


ELECTROLYTES  CONTAINING  ARSENIC. 


35 


fluence  upon  the  copper  deposits,  it  becomes  important  to  ascer- 
tain which  of  the  two  ions  (Na  ion  and  Cl  ion)  produces  this 
good  effect.  To  attain  this  object,  hydrochloric  acid,  which  has 
the  Cl  ion  in  common  with  sodium  chloride,  was  first  tried  and 
used  as  "  addition-agent "  in  this  experiment.  For  this  pur- 
pose, standard  hydrochloric  acid  solution  was  prepared  by  diluting 
10  c.c.  of  concentrated  acid  containing  37.5  per  cent.  HC1  to  100 
c.c.  A  measured  volume  of  this  solution  was  added  to  each 
electrolyte  so  that  it  contained  the  same  amount  of  chlorine,  per 
liter,  as  in  the  case  of  sodium  chloride,  that  is,  o.oi  per  cent, 
chlorine. 

It  may  be  noted  here  that  just  as  sodium  chloride  reacts  with 
the  cupric  sulphate  of  the  electrolyte,  so  hydrochloric  acid  reacts 
with  it,  to  form  cupric  chloride.  This  reaction  may  be  repre- 
sented by  the  following  equation : 

2HC1  plus  CuSO4  =  H2SO4  plus  CuCl2. 

So,  in  reality,  there  exists  in  the  electrolyte  cupric  chloride 
instead  of  hydrochloric  acid,  when  the  latter  is  added  to  the 
cupric  sulphate  electrolyte.  The  experimental  data  are  given  in 
Table  VI. 

TABLE  VI. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSO4-5H2O,  10  per  cent.  H2SO4,  and  o.oi  per  cent.  Cl  as  HC1. 
Anode  contained  1.15  per  cent.  As  and  1.12  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  deg.  Cent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elet;t. 
after  Run. 

Photo. 
VI. 

i  As. 

$Sb. 

%  As. 

$Sb. 

Series  A. 

A 

i 

1-5 

40 

0.49 

O.OO22 

O.OOO4 

1.83 

0.0070 

i 

2 

3-0 

40 

0.47 

O.O030 

0.0004 

3-24 

0.0036 

2 

3 

6.0 

40 

0.48 

O.OO74 

O.OO05 

6.04 

0.0080 

3 

4 

8.0 

40 

0.49 

O.OI06 

O.OOO4 

8.06 

0.0030 

4 

Series  B. 

B 

i 

i-5 

50 

0-45 

0.0015 

0.0009 

2.09 

0.0075 

i 

2 

3-0 

50 

0.44 

O.OOI4 

O.OOO2 

3.46 

0.0083 

2 

3 

6.0 

50 

0.44 

0.0037 

O.OOO7 

6.25 

0.0030 

3 

4 

8.0 

50 

0-44 

0.0023 

O.O007 

8.3I 

0.0030 

4 

The  deposits  formed  at  both  temperatures  (40°  C.  and  50°  C.) 
were  satisfactory.     Those  which  formed  at  40°  C.  were  bright, 


36  ELECTRO-DEPOSITION  OF  COPPER  FROM 

solid,  smooth,  slightly  crystalline  deposits,  free  of  "  trees,"  but 
nodular  at  their  edges,  whereas  the  deposits  formed  at  50°  C. 
were  similar  in  character,  but  brighter.  As  to  the  result  of  bend- 
ing test,  the  deposits  obtained  from  the  higher  temperature  ap- 
peared to  be  more  ductile  than  those  from  the  lower  tempera- 
ture, as  they  cracked  less  than  those  formed  at  40°  C.  When  the 
test-strips  of  deposits  no.  3  and  no.  4,  series  A,  were  hammered 
double,  they  cracked  at  the  outer  side  of  the  bend. 

Chemical  analyses  show  that  the  deposits   formed  at  40°   C. 


were  higher  in  arsenic  than  those  at  50°  C.  and  that  they  were 
not  so  pure  as  those  obtained  in  electrolytes  containing  sodium 
chloride. 

The  results  of  this  experiment,  therefore,  indicate  that  the  Cl 
ion  does  exert  a  beneficial  influence  upon  the  deposited  copper  and 
that  hydrochloric  acid  is  not  so  active  an  addition-agent  as  sodium 
chloride,  as  the  presence  of  the  latter  gives  cathode  copper  which 
is  purer  and  more  ductile.  Photograph  VI.  shows  the  character 
of  the  deposits. 


ELECTROLYTES  CONTAINING  ARSENIC. 


37 


Experiment  VII. 

As  Cl  ion  was  found  to  produce  a  good  effect  upon  the  depos- 
ited copper  and  to  prevent,  to  a  great  extent,  the  deposition  of 
arsenic  and  antimony,  it  now  remains  to  find  that  the  Na  ion 
would  produce  the  same  effect.  In  order  to  accomplish  this, 
sodium  sulphate  (Na2SO4-ioH2O)  was  selected  and  a  weighed 
amount  of  this  salt  added  to  each  electrolyte,  so  that  it  contained 
0.0065  Per  cent,  sodium,  which  corresponded  to  the  same  amount 
of  sodium  as  in  the  case  of  sodium  chloride  (Experiment  V.). 

Table  VII.  gives  the  results  of  this  experiment  and  Photograph 
VII.  shows  the  character  of  the  deposits. 

TABLE  VII. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSO4-sH2O,  10  per  cent.  HaSCX,  and  0.0065  per  cent.  Na  as  Na2SO4. 
Anode  contained  1.47  per  cent.  As  and  1.12  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  deg.  Cent. 

Average 
E.M.F. 

in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
VII. 

jf  As, 

0Sb. 

i  As. 

<Sb, 

Series  A. 

A 

i 

i-5 

40 

0.51 

0.0023 

0.0006 

1.86 

0.0017 

i 

2 

3-0 

40 

0.50 

0.0975 

0.1403 

3.36 

0.0090 

2 

3 

6.0 

40 

0.51 

0.0066 

0.0016 

6.16 

0.0084 

3 

4 

8.0 

40 

0.50 

0.0061 

0.0004 

8-44 

0.0060 

4 

Series  B. 

B 

i 

i-5 

50 

0-45 

O.OOII 

0.0005 

1.97 

0.0045 

i 

2 

3-0 

50 

0.46 

0.0023 

0.0003 

3-32 

O.OO2I 

2 

3 

6.0 

50 

0.44 

0.0018 

0.0002 

6.37 

0.0073 

3 

A 

R.O 

50 

0.46 

0.0063 

O.OOO4 

8-45 

O.OO56 

4 

The  deposits  which  formed  at  40°  C.  and  in  electrolytes  con- 
taining 1.5  per  cent.,  6  per  cent.,  and  8  per  cent,  arsenic  were 
found  bright,  solid,  and  absent  of  "  trees,"  while  the  deposit 
which  formed  at  the  same  temperature,  but  in  electrolyte  which 
contained  3  per  cent,  arsenic  was  very  bad,  exceedingly  brittle  and 
of  dull  color.  It  was  composed  not  only  of  nodular  crystals,  but 
of  dendritic  "trees"  formed  especially  at  the  edges,  as  clearly 
shown  in  No.  2,  Photograph  VII. ,  A. 

When  the  test-strips  of  deposits  of  series  A  were  hammered 
double  it  was  found  that  they  were  not  very  ductile,  as  deposits 
no.  3  and  no.  4  were  broken  into  two  and  deposit  no.  i  almost 
into  two. 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


The  deposits  which  formed  at  50°  C.  were  all  bright,  and  solid 
and  free  of  "  trees,"  though  a  few  small  rounded  nodules  formed 
on  the  surface.  The  bending  test  showed  that  these  deposits  were 
much  tougher  and  more  ductile  than  those  which  formed  at  40° 
C.,  for  the  test-strips  did  not  even  crack  when  they  were  ham- 
mered double. 

As  to  the  purity  of  the  deposited  copper,  it  will  be  observed  in 
Table  VII.  that  the  amount  of  arsenic  and  antimony  in  the  ca- 
thodes of  both  series  was  in  all  cases  low,  except  deposit  no.  2, 
series  A,  which  was  obtained  at  40°  C.  and  in  electrolyte  con- 
taining 3  per  cent,  arsenic.  It  contained  much  arsenic  and  anti- 


mony.  It  should  also  be  observed  that  the  amount  of  impurities 
contained  in  deposits  which  formed  at  40°  C.  was  notably  higher 
than  that  contained  in  those  which  formed  at  50°  C. 

From  what  has  been  said,  it  will  then  be  seen  that  the  presence 
of  a  small  amount  of  sodium  sulphate  in  the  electrolytes  had  a 
decidedly  good  effect,  chemically  and  physically,  upon  the  depos- 
ited copper ;  provided  that  the  electrolysis  be  conducted  at  50°  C. 


ELECTROLYTES  CONTAINING  ARSENIC. 


39 


At  40°  C,  however,  its  effect  was  somewhat  decreased  and  it  had 
practically  no  effect  upon  the  deposited  copper  when  the  electro- 
lyte contained  3  per  cent,  arsenic. 

As  to  the  relative  effectiveness  of  the  Na  ion  and  the  Cl  ion, 
the  former  appeared  to  be  less  effective  at  the  lower  temperatures, 
whereas  at  the  higher  temperature  the  beneficial  effect  of  the 
presence  of  either  of  the  ions  was  appreciably  the  same. 

Experiment  VIII. 

In  this  experiment  a  larger  amount  of  sodium  sulphate  was 
employed  than  in  Experiment  VII.  It  was  added  to  the  electro- 
lytes, with  the  object  of  ascertaining  whether  the  larger  amount 
would  produce  a  greater  effect  upon  the  deposited  copper.  The 
amount  added  was  100  times  that  which  was  used  in  Experiment 
VII. ;  in  other  words,  each  of  the  electrolytes  contained  0.65  per 
cent,  sodium. 

It  should  be  mentioned  here  that  during  the  electrolysis  the 
potential  difference,  particularly  in  the  lower  temperature  series, 
seemed  to  increase  slightly,  with  the  presence  of  this  large  amount 
of  sodium  sulphate. 

The  deposits  which  formed  at  both  temperatures  were  satisfac- 
tory. They  were  bright,  smooth,  tough  and  solid,  though  a  few 
small  rounded  nodules  scattered  on  the  surface.  Deposit  no.  2, 

TABLE  VIII. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSCX-sHaO,  10  per  cent.  H2S(X  and  0.65  per  cent.  Na  as  NaaSCX. 
Anode  contained  0.98  per  cent.  As  and  0.75  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Temp,  of 
Electrolyte 
in  deg.  Cent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
VIII. 

$  As. 

$Sb. 

$As. 

$Sb. 

Series  A. 

A 

i 

i-5 

40 

0-54 

O.OO20 

O.OO02 

1.85 

0.0040 

I 

2 

3-0 

40 

0.52 

O.OO5I 

O.OO28 

3-16 

O.OO2I 

2 

3 

6.0 

40 

0.51 

O.OO86 

O.OO06 

6.02 

0.0016 

3 

4 

8.0 

40 

0-54 

O.OIO4 

O.OOO2 

8.20 

0.0029 

4 

Series  B. 

B 

i 

i-5 

50 

0.44 

O.OOI3 

O.OOO4 

1.85 

0.0015 

i 

2 

3-0 

50 

0.44 

O.OOI8 

0.0004 

3.42 

0.0058 

2 

3 

6.0 

50 

0-45 

O.OOI9 

O.OOO6 

6.34 

0.0054 

3 

4 

8.0 

50 

0-45 

0.0023 

0.0007 

8.05 

0.0032 

4 

4O  ELECTRO-DEPOSITION  OF  COPPER  FROM 

series  A,  was  the  most  nodular.  The  bending  test  showed  that 
they  were  ductile  and  that  those  formed  at  the  higher  tempera- 
ture were  more  ductile  than  those  formed  at  the  lower  tem- 
perature. 

The  chemical  analyses  show  that  the  deposits  formed  at  40°  C. 
contained  higher  percentage  of  arsenic  than  those  which  formed 
at  50°  C.,  while  the  percentages  of  antimony  in  both  series  were 
low,  except  no.  2,  series  A,  which  contained  a  much  greater  per- 
centage than  the  rest.  The  experimental  data  of  this  experiment 


are  given  in  Table  VIII.  and  the  character  of  the  deposits  is 
shown  in  Photograph  VIII. 

Comparing  the  results  with  those  obtained  in  Experiment  VII. , 
it  is  found  that  the  larger  amount  of  sodium  sulphate  added  to 
the  electrolytes  does  not  appear  to  have  much  improved  the  copper 
deposits  of  either  series,  except  the  deposit  which  formed  at  40° 
C.  and  in  electrolyte  containing  3  per  cent,  arsenic,  in  which  case 
it  hindered,  to  a  great  extent,  the  precipitation  of  arsenic  and 
antimony. 


ELECTROLYTES  CONTAINING  ARSENIC. 


It  is,  therefore,  obvious  from  the  results  of  the  two  experi- 
ments (VII.  and  VIII.)  that  at  50°  C.  the  presence  of  a  small 
amount  of  sodium  sulphate  had  a  decidedly  good  effect  on  the 
deposited  copper  in  all  cases,  whereas  at  40°  C.  such  a  small 
amount  had  the  same  effect,  but  no  effect  in  the  case  in  which  the 
electrolyte  contained  3  per  cent,  arsenic,  unless  a  sufficiently  large 
amount  was  present.  The  higher  temperature  is,  therefore,  pref- 
erable, as  it  does  not  only  cause  the  deposited  copper  to  form 
more  ductile,  but  also  renders,  in  this  case,  the  "  addition-agent " 
more  effective. 

Experiment  IX.  A. 

The  electrolytes  used  in  this  experiment  contained  only  3  per 
cent,  and  6  per  cent,  arsenic,  as  the  electrolysis  was  conducted 
only  at  50°  C.  The  "  addition-agents "  tried  were  aluminium 
sulphate  (Al2(SO4)3-i8H2O)  and  aluminium  chloride  (A1C13- 
6H2O).  In  either  case,  the  amount  of  salt  added  was  such  that 
the  electrolyte  contained  o.io  per  cent.  Al. 

TABLE  IX.  A. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSO4-5H2O  and  10  per  cent.  H2SO4.  Temperature  of  Electrolyte 
50°  C.  Anode  contained  0.97  per  cent.  As  and  0.89  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 

Electrolyte. 

Addition-Agent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in 
Elect,  after  Run. 

Photo. 
IX.  A. 

A12(S04)3 
$  in  Al. 

A1C18 

$  in  Al. 

^As. 

$Sb. 

^As. 

^Sb. 

I 
2 

*3 
*4 

3-0 
6.0 
3-0 
6.0 

O.IO 
O.IO 

0.47 
0.47 
0-45 
0-43 

O.OO28 
O.OO5O 
0.0030 
0.0087 

0.0003 
O.OO03 
0.0004 
0.0004 

3-44 
6.48 
3.08 
5-92 

0.0061 
0.0095 
0.0081 
0.0041 

I 
2 

3 

4 

O.IO 
O.IO 

*  The  bad  copper  first  deposited  was  filed  off  before  the  samples  were 
taken  for  analysis. 

It  should  be  mentioned  here  that  at  the  beginning  of  the  elec- 
trolysis, a  peculiar  effect  was  observed  in  the  case  in  which  alumi- 
nium chloride  was  used.  A  white  layer,  which  appeared  to  be 
oxide  of  arsenic  formed  on  the  cathode  surface,  as  soon  as  elec- 
trolysis began,  and  in  the  course  of  a  few  hours  became  dark-red. 
During  the  formation  of  this  layer  the  potential  difference  was 


42 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


high,  reading  from  0.58  to  0.60  volt.  After  a  period  of  fifteen 
hours  the  deposited  copper,  however,  began  to  improve,  giving  a 
bright  surface.  This  action  of  aluminium  chloride  is  difficult  to 
explain  at  present,  unless  it  precipitated  arsenic  from  solution  at 
the  first  period  of  the  run.  A  satisfactory  explanation  may  be 
had  with  further  investigations.  But,  suffice  it  to  say  that  the 
strange  effect  might  be  due  to  the  presence  of  an  excessive  amount 
of  aluminium  chloride  in  the  electrolyte ;  these  electrolytes,  at  the 
end  of  the  run,  contained  less  arsenic  than  those  to  which  alumi- 
nium sulphate  was  added. 

The  two  deposits  from  electrolytes  containing  aluminium  chlo- 


ride were  found  each  to  consist  of  two  layers.  The  layer  first 
deposited  was  bad,  brittle  and  incoherent,  while  the  other  layer, 
on  the  contrary,  was  bright,  smooth,  and  quite  coherent.  The 
analytical  results  of  no.  3  and  no.  4,  Table  IX.  A,  show  that  both 
of  these  layers  were  low  in  arsenic  and  antimony.  The  character 
of  these  two  deposits  are  shown  in  Photograph  IX.  A,  marked 
3  and  4. 

With  aluminium  sulphate  in  the  electrolytes  no  such  action  as 


ELECTROLYTES  CONTAINING  ARSENIC. 


43 


that  of  aluminium  chloride  was  observed.  The  presence  of  alumi- 
nium sulphate  rendered  the  deposited  copper  bright,  solid  and 
coherent,  and  prevented  the  deposition  of  arsenic  and  antimony, 
as  is  clearly  shown  in  Table  IX.  A,  no.  I  and  no.  2.  The  deposits 
also  possessed  great  ductility,  which  the  test-strips  indicated,  when 
they  were  hammered  double. 

Experiment  IX.  B. 

With  a  view  to  determining  the  relative  effect  of  a  larger  or  a 
smaller  amount  of  sodium  chloride  upon  copper  deposits,  this 
experiment  was  performed  with  electrolytes  of  the  same  compo- 
sition as  was  used  in  Experiment  IX.  A,  but  with  the  addition 
of  two  different  amounts  of  sodium  chloride.  In  the  one  case 
the  amount  of  salt  added  was  such  that  the  electrolyte  contained 
0.05  per  cent.  Cl,  and  in  the  other  case  the  electrolyte  was  made 
to  contain  twice  as  much,  that  is  to  say,  o.io  per  cent.  Cl. 

The  deposits  from  both  cases  were  similar  in  character,  but 
those  from  electrolytes  containing  less  sodium  chloride  appeared 
to  be  little  better,  particularly  in  color.  All  the  deposits  were 
bright,  solid,  smooth  and  free  of  nodules,  but  they,  as  compared 
with  those  obtained  from  electrolytes  which  contained  only  o.oi 
per  cent.  Cl  (Experiment  V.)  seemed  to  be  a  little  inferior  in 
physical  properties,  that  is,  less  bright,  less  smooth  and  less 
ductile. 

The  result  of  bending  test  showed  that  the  deposits  from  elec- 
trolytes containing  0.05  per  cent.  Cl  were  more  ductile  than  those 


TABLE  IX.  B. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSO4-5H2O  and  10  per  cent.  HoSCX  Temperature  of  Electrolyte 
50°  C.  Anode  contained  0.97  per  cent.  As  and  0.89  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Addition-Agent 
NaCl. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in 
Elect,  after  Run. 

Photo. 
IX.  B. 

%  in  Cl. 

— 

«£As. 

$Sb. 

°k  As. 

$Sb. 

I 
2 

3 

4 

3-0 
6.0 
3-0 
6.0 

O.IO 
O.IO 

0.05 
0.05 

0-43 
0.42 
0.41 
0.41 

O.OO22 
O.OO48 
O.OO2O 
0.0018 

0.0004 
0.0007 
0.0008 
0.0003 

3-50 
6.48 
3-41 
6.41 

0.0078 
0.0064 
0.0223 
0.0190 

I 
2 

3 

4 



44  ELECTRO-DEPOSITION  OF  COPPER  FROM 

which  formed  in  electrolytes  containing  o.io  per  cent.,  as  the  test- 
strips  of  the  latter  cracked  almost  in  two,  while  those  of  the 
former  did  not  crack,  when  they  were  hammered  double. 

The  purity  of  the  deposits  was  in  all  cases  high,  but  was  not  so 
high  as  those  from  electrolytes  which  contained  o.oi  per  cent.  Cl 
as  sodium  chloride,  when  the  electrolysis  was  conducted  under 
similar  conditions.  The  results  of  this  experiment  are  expressed 
in  Table  IX.  B,  and  the  character  of  the  deposits  are  shown  in 
Photograph  IX.  B. 

From  the  results  of  this  experiment  and  those  of  Experiment 
V.,  series  B,  it  will  be  seen  that  the  presence  of  a  greater  amount 
of  sodium  chloride  in  the  electrolyte  proved  to  be  less  beneficial 
on  the  deposited  copper.  Therefore,  when  sodium  chloride  is 
used  to  improve  the  character  of  the  deposits  and  to  prevent  the 
deposition  of  arsenic  and  antimony,  the  amount  added  to  the  elec- 
trolyte seems  to  be  better  limited  to  not  more  than  o.oi  per 
cent.  Cl. 

ELECTROLYTES  WHICH  CONTAINED  ORGANIC  "ADDITION-AGENTS." 

In  this  series  of  experiments,  the  organic  "  addition-agents " 
tried  were  gelatine,  tannin  and  peptone  (E.  &  A.  from  meat)  and 
the  electrolyses  were  conducted  with  electrolytes  of  the  following 
composition : 

(a)  Electrolyte  containing  15  per  cent.  CuSO4-5H2O,  10  per 
cent.  H2SO4  plus  3  per  cent,  arsenic  and  o.oi  per  cent,  organic 
addition-agent. 

(b)  Electrolyte  containing  15  per  cent.  CuSO4-5H2O,  10  per 
cent.  H2SO4  plus  6  per  cent,  arsenic  and  o.oi  per  cent,  organic 
addition-agent. 

(c)  Electrolyte  containing  15  per  cent.  CuSO4-5H2O,  10  per 
cent.  H2SO4  plus  3  per  cent,  arsenic  and  0.02  per  cent,  organic 
addition-agent. 

(d)  Electrolyte  containing  15  per  cent.  CuSO4-5H2O,  10  per 
cent.  H2SO4  plus  6  per  cent,  arsenic  and  0.02  per  cent,  organic 
addition-agent. 

The  gelatine  and  tannin  were  each  prepared  by  dissolving  5 
grams  in  a  small  quantity  of  boiling  water.  The  solution  was 
then  diluted  to  200  c.c.  which  contained  2.5  per  cent,  of  the  rea- 
gent. The  solution  of  peptone  was  prepared  in  the  same  way, 


ELECTROLYTES  CONTAINING  ARSENIC.  45 

but  dissolved  in  a  larger  quantity  of  water  (about  350  c.c.)  and 
diluted  to  400  c.c,  for  peptone  is  not  so  soluble  as  the  other  two 
organic  substances.  The  solution  contained  1.25  per  cent,  peptone. 

Experiment  X. 

In  this  experiment  gelatine  and  tannin  were  used  as  "  addition- 
agents/'  and  the  amount  added  in  each  case  was  such  that  the 
electrolytes  contained  one  part,  by  weight,  of  the  "  addition-agent " 
to  10,000  parts  of  electrolyte,  and  one  part  to  5,000  parts,  that  is 
to  say,  the  electrolytes  contained  o.oi  per  cent,  and  0.02  per  cent, 
of  the  organic  "  addition-agent." 

With  the  presence  of  gelatine  in  the  electrolyte  it  was  observed 
that  during  the  first  few  hours  of  electrolysis  the  gelatine  had 
strange  effect  upon  the  deposited  copper,  as  small  "  trees  "  which 
are  shown  in  C,  Photograph  X.,  were  formed  in  every  case  all 
over  the  cathode  surface  and  particularly  at  the  edges.  With  the 
higher  proportion  of  gelatine  in  the  electrolytes,  the  more  and 
larger  the  "  trees/'  some  of  which  grew  as  long  as  half  an  inch 
at  the  end  of  fifteen  hours'  electrolysis.  At  this  period  the  cathodes 
were  withdrawn  and  the  "  trees  "  knocked  off.  The  cathodes  were 
again  placed  in  the  original  position,  but  with  the  reverse  sides 
front,  in  order  to  ascertain  whether  the  gelatine  had  the  same 
effect  after  fifteen  hours'  electrolysis.  It  was,  however,  surpris- 
ing to  find  that  it  behaved  entirely  differently.  The  copper  depos- 
ited from  this  time  on  was  observed  to  be  perfectly  smooth,  and 
neither  "  trees  "  nor  nodules  were  formed  on  the  cathode  surface. 

Another  fact  that  was  also  observed  during  the  electrolysis  was 
that  the  presence  of  gelatine  caused  the  potential  difference  much 
higher,  an  average  of  about  0.04  to  0.08  volt,  and,  as  the  electro- 
lysis continued,  it  gradually  diminished. 

From  the  two  facts  mentioned  above,  it  appears  that  gelatine, 
as  the  result  of  electrolysis,  undergoes  a  chemical  change  and  the 
product,  or  products,  thus  formed,  must  have  produced  such  a 
beneficial  influence  as  not  only  to  prevent  the  formation  of  "  trees  " 
and  the  deposition  of  arsenic  and  antimony,  but  also  to  cause  the 
deposited  copper  to  form  smooth,  and  tough. 

With  tannin  in  the  electrolyte,  the  copper  deposited  was  ob- 
served to  be  perfectly  smooth  throughout  the  run,  and  after  fifteen 
hours'  electrolysis  the  cathodes  were  turned  reverse  side  front,  in 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


the  same  manner  as  in  the  case  of  those  in  the  electrolytes  con- 
taining gelatine.  This  was  done  in  order  to  show  whether  tannin 
would  produce  different  effect  on  the  deposited  copper  after  a 
period  of  electrolysis.  The  presence  of  tannin  in  the  electro- 
lytes did  not  raise  the  potential  difference  to  any  extent,  and  it 
was  in  every  case  lower  than  the  electrolytes  which  contained 
gelatine. 

After  forty-two  hours'  run,  the  deposited  copper  formed  in  elec- 
trolytes containing  tannin,  in  each  case,  was  observed  to  become 
sprangling  and  the  crystals  appeared  to  have  sharp  edges,  which 
might  be  due  to  the  "  addition-agent "  having  been  consumed. 
At  this  period  a  further  addition  of  tannin  was,  therefore,  made 
and  the  amount  added  to  each  cell  was  the  same  as  originally 
present.  But  this  addition  did  not  seem  to  cause  any  apparent 
improvement  of  the  deposits. 

The  results  of  this  experiment  are  recorded  in  Table  X. 

TABLE  X. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSCV5H2O  and  10  per  cent.  tLSCX.  Temperature  of  Electrolyte 
50°  C.  Anode  contained  1.06  per  cent.  As  and  i.oi  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 

Addition-  Agent. 

Average 
E.M.F. 

Impurities  in  De- 
posited Copper. 

Impurities  in 
Elect,  after  Run. 

Photo. 

x 

Electrolyte. 

0  Gela- 
tine. 

#  Tan- 
nin. 

in  Volt. 

<£As. 

#Sb. 

$  As. 

^Sb. 

Series 

A. 

A 

i 

3-0 

0.01 



0.48 

0.0013 

O.OOO3 

3-19 

0.0023 

i 

2 

6.0 

O.OI 



0.48 

O.OOlS 

0.0003 

6.ii 

0.0023 

2 

3 

3-0 

O.02 



0.48 

O.OOOQ 

0.0003 

3-17 

0.0019 

3 

4 

6.0 

O.O2 



0.50 

O.OO20 

0.0007 

5-97 

0.0062 

4 

Series 

B. 

B 

i 

3-0 



O.OI 

0.46 

0.0020 

O.OOO2 

3-12 

0.0023 

i 

2 

6.0 



O.OI 

0-45 

0.0015 

0.0003 

6.18 

0.0033 

2 

3 

3-0 



0.02 

0.41 

O.OOI2    O.O002 

3-25 

0.0039 

3 

4 

6.0 



0.02 

0-45 

0.0017    O.O002 

6.16 

0.0042 

4 

The  deposits,  series  A,  which  formed  in  electrolytes  contain- 
ing gelatine  were  very  bright  and  solid,  perfectly  smooth  and 
coherent,  and  composed  of  very  fine  grains.  They  also  possessed 
very  high  ductility,  as  the  test-strips  did  not  crack  nor  show  even 
signs  of  cracking  when  doubled  and  hammered  flat. 


ELECTROLYTES  CONTAINING  ARSENIC. 


47 


The  physical  and  mechanical  properties  of  the  deposits,  series 
B,  which  formed  in  the  presence  of  tannin  were  similar  to  those 
of  series  A,  except  that  the  grains  of  the  deposits  were  coarse  and 
more  pronounced.  They  possessed  very  high  ductility,  similar  to 
deposits  from  electrolytes  which  contained  gelatine.  Photograph 
X.  shows  the  character  of  the  deposits  of  these  two  series. 

The  purity  of  the  deposited  copper  from  both  series  was,  in 


every  case,  extraordinarily  high.  The  analyses  show  that  they 
contained,  in  no  case,  more  than  0.002  per  cent,  arsenic  and  0.0007 
per  cent,  antimony. 

From  what  has  been  said  regarding  the  physical  and  chemical 
properties  of  the  deposits  obtained  from  both  series,  it  will  be 
seen  that  the  presence  of  gelatine  in  the  electrolytes,  though,  at 
start,  it  caused  the  formation  of  small  "trees,"  produced  a  re- 
markably beneficial  effect  upon  the  deposited  copper  and  that 
the  effect  of  tannin  was  very  much  the  same.  Both  of  these 
organic  "  addition-agents "  rendered  the  deposits  smooth,  very 
ductile,  and  finely  crystalline,  and  were  very  effective  in  pre- 
venting the  deposition  of  arsenic  and  antimony.  Of  these  two 


48 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


organic  substances,  tannin  seemed  to  be  the  more  preferable.     No 
"  trees  "  formed  at  the  start  of  the  electrolysis. 

Experiment  XL  A. 

Peptone  (from  meat)  was  employed  in  this  experiment  as 
"  addition-agent,"  the  amount  of  which  added,  at  the  start,  to 
the  electrolytes  was  in  the  same  proportion  as  gelatine  and  tannin 
in  the  preceding  experiment,  that  is,  one  part,  by  weight,  of  pep- 
tone in  10,000  parts,  and  5,000  parts  of  each  electrolyte. 

It  may  be  stated  here  that  the  presence  of  peptone  produced 
a  strange  and  bad  influence  on  the  deposited  copper.  Small 


"  trees  "  formed  at  the  beginning  of  the  run,  which  looked  like 
those  formed  at  the  start  in  electrolytes  containing  gelatine,  but 
more  of  dull  color.  After  an  interval  of  fifteen  hours  from  the 
beginning  of  the  electrolysis,  the  cathodes  were  withdrawn  and, 
after  the  "  trees  "  at  the  edges  were  knocked  off,  again  placed 
in  the  original  position  but  with  the  reverse  sides  front,  in  order 
to  ascertain  whether  the  peptone,  as  in  the  case  of  gelatine,  would 


ELECTROLYTES  CONTAINING  ARSENIC. 


49 


behave  differently.  A  further  addition  of  the  peptone  was  made 
at  this  time — same  amount  as  originally  present  in  each  cell. 
During  the  three  hours  after  this  addition,  the  surface  of  the 
cathodes  seemed  to  be  smooth  and  spangling,  but  soon  the  same 
kind  of  "  trees  "  began  to  appear,  continued  to  grow,  and  became 
large  and  long  at  the  end  of  the  run,  as  shown  in  Photograph 
XL  A. 

Another  fact  that  was  observed  during  the  electrolyses  is  that 
the  potential  differences  between  the  electrodes  in  each  case 
dropped  greatly,  but  gradually,  and  whenever  an  addition  of 
peptone  was  made  the  potential  difference  was  increased  from 
0.06  to  0.08  volt.  This  shows  that  the  drop  of  voltage  was  an 
indication  of  the  consumption  of  the  organic  "  addition-agent." 
In  order,  -then,  to  maintain  a  certain  amount  of  peptone  present 
in  the  electrolytes,  it  became  necessary  to  add  a  certain  amount  at 
such  intervals  as  the  drop  of  voltage  was  observed.  Two  further 
additions  were  made,  and  the  amount  added  each  time  to  the  cells 
was  in  the  proportion  of  one  part,  by  weight,  of  original  "  addi- 
tion-agent "  to  5,000  parts  of  electrolyte. 

The  results  of  this  experiment  are  recorded  in  Table  XL  A, 


TABLE  XL  A. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSO4-sH2O,  10  per  cent.  H2S(X  Temperature  of  Electrolyte  50°  C. 
Anode  contained  0.96  per  cent  As  and  0.96  per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 

Electrolyte. 

Per  Cent,  of 
Peptone  in 
Electrolyte. 

Average 
E.M.F. 

in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
XI.  A. 

^As. 

*Sb. 

4  As. 

*Sb. 

I 

3-0 

O.OI 

0.38 

0.0478 

0.0035 

3-31 

0.0026 

I 

2 

6.0 

O.OI 

0.40 

0.0521 

0.0029 

6.10 

0.0026 

2 

3 

3-0 

O.O2 

0-39 

0.0552 

0.0057 

3-12 

0.0016 

3 

4 

6.0 

0.02 

0-39 

0.0437 

0.0025 

6.21 

0.0032 

4 

and  the  character  of  the  deposits  are  shown  in  Photograph  XL  A. 
All  the  deposits  from  this  experiment  were  not  at  all  satisfac- 
tory: they  were  exceedingly  brittle  and  their  color  was  dark; 
they  were  also  composed  of  coarse  crystals  loosely  adhered  and 
dendritic  "  trees/'  easily  detached.  The  latter  interfered  with 
the  electrolysis  and  greatly  decreased  the  resistance  of  the  elec- 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


trolyte  between  the  electrodes,  thus  causing  the  average  potential 
difference  to  become  low,  as  shown  in  Table  XL  A. 

As  to  the  amount  of  impurities  in  the  deposits,  they  all  ran 
high,  both  in  arsenic  and  in  antimony,  which  impaired  the  physical 
properties  of  the  deposited  copper. 

According  to  the  results  of  this  experiment,  peptone  alone  is 
not  at  all  a  satisfactory  "  addition-agent "  and  is,  therefore,  not 
suitable  to  use  in  electrolytic  refining.  With  a  cupric  sulphate 
electrolyte  it  causes  not  only  the  injurious  impurities  to  deposit 
with  the  copper,  but  also  the  copper  is  deposited  as  individual 
crystals  and  dendrites,  which  is  a  very  brittle  mass. 

ELECTROLYTES  WHICH   CONTAINED  ORGANIC  AND  INORGANIC 
"ADDITION-AGENTS." 

In  this  series  of  experiments,  the  composition  of  electrolytes 
was  the  same  as  the  composition  of  those  which  contained  an 
organic  "  addition-agent,"  but  with  the  presence  of  an  inorganic 
"  addition-agent." 

Experiment  XL  B.  * 

In  the  same  way  and  with  the  same  amounts  of  peptone  added 
to  the  electrolytes  at  the  same  different  intervals  of  time,  this 
experiment  was  performed,  as  Experiment  XL  A,  but  with  an 
amount  of  sodium  chloride  added,  to  give  the  presence  of  o.oi 
per  cent.  Cl.  The  results  are  given  in  Table  XL  B,  and  the  char- 
acter of  the  deposit  is  shown  in  Photograph  XL  B. 

TABLE  XI.  B. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSOvSHaO,  10  per  cent.  H2SO4,  and  o.oi  per  cent.  Cl  as  XaCl. 
Temperature  of  Electrolyte  50°  C.  Anode  contained  0.96  per  cent.  As 
and  0.96  per  cent.  Sb. 


No.  of 
Ceils. 

Per  Cent, 
of  As  in 
Electrolyte. 

Per  Cent,  of 
Peptone  in 
Electrolyte. 

Average 
E.M.F. 

in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in  Elect, 
after  Run. 

Photo. 
XI  B. 

4  As. 

^Sb. 

#As. 

^Sb. 

I 

3-0 

O.OI 

0.48 

O.OOII 

O.OOO2 

3-24 

0.0026 

I 

2 

6.0 

O.OI 

0.49 

O.O020 

O.OOOI 

6.10 

0.0022 

2 

3 

3-0 

O.02 

0.47 

O.OOO8 

O.O002 

3-36 

0.0013 

3 

4                 6.0 

O.O2 

0.49 

0.0017 

O.OOOI       6.18 

0.0008 

4 

ELECTROLYTES  CONTAINING  ARSENIC.  51 

It  is  rather  surprising  to  see  that  the  deposits  obtained  from 
electrolytes  containing  the  combined  "  addition-agents "  of  pep- 
tone and  sodium  chloride  were  very  satisfactory,  while  those 
obtained  from  electrolytes  containing  peptone  alone  were,  as  has 
been  previously  mentioned,  very  rough  and  impure.  A  compari- 
son of  the  deposits  shown  in  Photograph  XL  A  and  XL  B  will 
show  the  difference  in  their  character.  With  the  sodium  chlo- 
ride and  peptone  the  deposits  were  very  good  as  regards  their 
physical  and  chemical  properties :  they  were  hard,  bright,  smooth 
and  finely  crystalline.  As  to  their  ductility,  they  were  found  to 
be  less  ductile  than  those  obtained  from  electrolytes  which  con- 
tained the  same  amount  of  sodium  chloride  alone,  as  "  addition- 
agent,"  as  the  test-strips  were  broken  in  two  pieces,  except  no.  3, 
which  cracked  almost  in  two,  when  they  were  bent  double.  The 
chemical  analyses  show  that  their  purity  was  exceptionally  high 
in  all  cases,  and  that  none  of  them  contained  more  than  0.002 
per  cent,  arsenic  and  0.0002  per  cent,  antimony. 

Thus  it  is  evident  that  the  presence  of  a  small  amount  of  sodium 
chloride  counteracted  the  bad  or  injurious  effect  of  peptone,  and 
that  the  combined  action  of  these  two  "  addition-agents "  was 
beneficial,  since  it  rendered  the  deposits  to  become  smooth,  solid 
and  pure.  Moreover,  peptone  with  the  presence  of  sodium  chlo- 
ride seemed  to  increase  the  hardness  of  the  deposits,  and,  as 
evidence,  there  may  be  cited  the  fact  that  the  copper  deposited 
at  the  beginning  of  the  electrolysis  was  so  hard  that  it  caused 
the  starting-sheets  to  bend  inward,  top  and  bottom. 

Experiment  XII. 

This  experiment  was  conducted,  as  usual,  in  two  series, 
A  and  B.  The  combined  "  addition-agents  "  for  the  former  series 
were  gelatine  and  sodium  chloride,  and  those  for  the  latter  series 
were  tannin  and  sodium  chloride.  The  electrolytes  for  both  series 
were  to  contain,  at  the  start,  the  same  proportion  of  organic 
"  addition-agents "  as  in  Experiment  X.,  that  is,  one  part  by 
weight,  in  10,000  parts  (o.oi  per  cent.)  and  one  part  in  5,000 
parts  (0.02  per  cent.)  of  electrolyte,  and  o.oi  per  cent.  Cl,  as 
sodium  chloride.  The  composition  of  the  electrolytes  and  the 
results  obtained  are  recorded  in  Table  XII.,  and  the  character  of 
the  deposits  is  shown  in  Photograph  XII. 


ELECTRO-DEPOSITION  OF  COPPER  FROM 


TABLE  XII. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuS(V5H2O,  10  per  cent.  H2SO4,  and  o.oi  per  cent.  Cl  as  NaCl. 
Temperature  of  Electrolyte  50°  C.  Anode  contained  1.17  per  cent.  As 
and  1.32  per  cent  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 
Electrolyte. 

Addition-Agent. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  De- 
posited Copper. 

Impurities  in 
Elect,  after  Run. 

Photo. 
XII. 

$  Gela- 
tine. 

<£  Tan- 
nin. 

%  As. 

^Sb. 

.A, 

*Sb. 

Series 

A. 

A 

i 

3-0 

O.OI 



0.48 

O.OOO8 

O.OOO2 

3-38 

0.0054 

I 

2 

6.0 

O.OI 



0.47 

O.OOI5 

0.0003 

6.51 

0.0043 

2 

3 

3-0 

O.02 



0.46 

O.OOO7 

0.0003 

3-32 

0.0054 

3 

4 

6.0 

O.O2 



0.50 

0.0009 

0.0003 

6.28 

0.0023 

4 

Series 

B. 

B 

i 

3-0 



O.OI 

0-43 

0.0014 

O.OOO2 

3-91 

0.0016 

'    i 

2 

6.0 



O.OI 

0.44 

0.0024 

O.O002 

6.47 

0.0013 

2 

3 

3-o 



O.O2 

0.44 

O.OOII 

O.OOO3 

3.38 

0.0019 

3 

4 

6.0 



0.02 

0-43 

0.0026 

O.O002 

6.49 

0.0033 

4 

The  deposits  from  series  A,  that  is,  from  electrolytes  which 
contained  the  combined  "  addition-agents  "  of  gelatine  and  sodium 
chloride,  were,  in  every  case,  very  satisfactory  and  similar  to 
those  obtained  from  electrolytes  containing  gelatine  alone  as 
"  addition-agent."  They  were  very  bright,  exceedingly  solid,  per- 
fectly smooth  and  finely  crystalline,  and  the  results  of  bending 
tests  showed  that  they  possessed  high  ductility,  as  the  test-strips, 
when  beaten  double,  did  not  even  show  signs  of  cracking. 

Their  chemical  properties  also  proved  just  as  satisfactory  as 
their  physical  properties.  The  analyses  show  that  the  amount  of 
impurities  in  the  deposited  copper  was,  in  each  case,  exceedingly 
small,  running  from  0.0007  per  cent,  to  0.0015  per  cent,  arsenic, 
and  from  0.0002  per  cent,  to  0.0003  Per  cent-  antimony,  which  is 
far  below  the  required  limit  for  the  best  commercial  copper. 

Here  the  fact,  as  has  been  pointed  out  in  Experiment  X.,  may 
be  recalled  that  small  dendritic  "  trees  "  were  formed  at  the  begin- 
ning of  the  electrolysis,  when  gelatine  was  alone  present  in  the 
electrolytes.  But  it  was  found  in  this  experiment,  with  sodium 
chloride  present,  that  no  such  "  trees  "  were  formed,  and,  on  the 
other  hand,  the  copper  first  deposited  was  rendered  perfectly 


ELECTROLYTES  CONTAINING  ARSENIC. 


53 


smooth.  This  brings  out  the  fact  that  the  presence  of  sodium 
chloride  hindered  the  formation  of  dendritic  "  trees,"  which  would 
have  been  formed,  if  the  sodium  chloride  were  absent  and  gelatine 
alone  present  in  the  electrolytes.  From  this  it  will  be  seen  that 
an  addition  of  a  small  amount  of  sodium  chloride  to  the  electro- 
lytes is  quite  necessary  and  important,  if  gelatine  is  used  to 
improve  the  copper  deposits. 

The  potential  difference  was  observed  to  be  high  with  the  pres- 


ence of  gelatine  in  the  electrolytes :  but  as  electrolysis  continued  it 
gradually  dropped,  as  in  the  previous  experiment.  After  80 
hours'  electrolysis,  a  second  addition  of  the  organic  "  addition- 
agents  "  was  made  in  both  series,  A  and  B,  and  the  amounts  added 
in  both  cases  were  the  same  as  originally  present. 

The  deposits  from  series  B,  that  is,  from  electrolytes  which  con- 
tained tannin  and  sodium  chloride,  were  also  satisfactory,  but  to 
a  slightly  less  degree  than  those  obtained  from  the  above  case, 
as  they  consisted  of  coarse  but  coherent  grains  with  sharp  edges. 
Their  physical  properties,  however,  were  similar  to  those  of 
series  B,  Experiment  X.,  that  is,  those  from  electrolytes  which 


54  ELECTRO-DEPOSITION  OF  COPPER  FROM 

contained,  as  "  addition-agent,"  only  tannin.  With  sodium 
chloride  present,  their  ductility  was  more  or  less  diminished,  for 
test-strips  from  all  deposits  except  no.  3,  series  B,  were  broken, 
when  they  were  hammered  double. 

Though  the  presence  of  sodium  chloride  with  tannin  in  the 
electrolytes  decreased  the  ductility  of  the  deposits,  it  did  not  seem 
to  affect  their  chemical  property  to  any  appreciable  extent,  as  the 
chemical  analyses  show  that  they  were  all  very  low  in  arsenic  and 
antimony.  The  potential  difference  was  lower  than  that  of  series 
A,  and  remained  practically  constant  throughout  the  run. 

From  what  has  been  said  in  regard  to  series  B,  it  will  be  seen 
that  an  addition  of  sodium  chloride  does  not  seem  necessary, 
when  tannin  is  used,  for  tannin  alone  appears  to  improve  the 
physical  properties  of  the  deposits  more  effectively  than  when 
sodium  chloride  is  also  an  associate. 

Experiment  XIII.  A. 

In  this  experiment  the  combined  "  addition-agents  "  used  were 
peptone  and  hydrochloric  acid,  and  gelatine  and  hydrochloric  acid. 
The  object  of  using  hydrochloric  acid  was  to  ascertain  the  effect 
of  Cl  ion  in  the  presence  of  either  of  the  organic  substances  men- 
tioned above.  The  electrolysis  was  conducted  in  four  cells,  two 
for  each  of  the  combined  "addition-agents."  The  electrolytes 
were,  in  each  case,  to  contain,  at  the  start,  one  part,  by  weight, 
of  the  original  "addition-agent"  in  5,000  parts  of  the  electrolyte 
(0.02  per  cent.)  and  o.oi  per  cent.  Cl,  as  hydrochloric  acid,  the 
preparation  of  which  was  made  in  the  same  manner  as  in  Experi- 
ment VI.  The  composition  of  the  electrolytes  and  the  results 
obtained  are  expressed  in  Table  XIII.  A.  and  the  character  of  the 
deposits  is  shown  in  Photograph  XIII.  A.  Deposits  no.  I  and  no. 
2  were  obtained  from  electrolytes  containing  peptone  and  hydro- 
chloric, and  deposits  no.  3  and  4  from  electrolytes  containing  gela- 
tine and  hydrochloric  acid. 

During  the  electrolysis  it  was  observed  that  the  potential 
difference  in  each  case  was  high  and  about  the  same  as  that  of 
Experiment  XL  B  and  Experiment  XII.,  when  gelatine  and 
sodium  chloride  were  used.  And  in  the  same  way,  the  potential 
difference  gradually  dropped,  as  electrolysis  proceeded.  This 
drop  of  voltage,  it  is  believed,  ascertained  the  consumption  of  the 


ELECTROLYTES  CONTAINING  ARSENIC. 


55 


TABLE  XIII.  A. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSO4,  10  per  cent.  H2SO4,  and  o.oi  per  cent.  Cl  as  HC1.  Temper- 
ature of  Electrolyte  50°  C.  Anode  contained  1.30  per  cent.  As  and  1.27 
per  cent.  Sb. 


No.  of 
Cells. 

Per  Cent, 
of  As  in 

Electrolyte. 

Per  Cent, 
of  Gelatine. 

Per  Cent, 
of  Peptone. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  Deposited 
Copper. 

Photo. 
XIII.  A. 

$As. 

$Sb. 

I 
2 

3 

4 

3-0 
6.0 
3-0 
6.0 

0.02 
O.O2 

O.O2 
0.02 

0.52 
0.49 
0.48 
0.49 

O.OO28 
0.0030 
0.0016 
0.0022 

0.0003 
0.0004 
0.0003 

O.OOO2 

I 
2 

3 

4 

original  substance.  Three  further  additions  of  the  organic 
"  addition-agents  "  were  made  in  each  case  during  the  run,  at  such 
intervals  as  deemed  necessary,  in  order  to  make  up  the  deficiency. 

With  peptone  and  hydrochloric  acid  in  the  electrolytes  it  was 
observed  that  the  copper  first  deposited  was  perfectly  smooth  and 
so  hard,  as  in  the  case  where  sodium  chloride  and  peptone  were 
present,  that  the  starting-sheets  were  caused  to  bend  slightly 
inward,  top  and  bottom.  But,  in  the  course  of  about  15  hours, 
small  rounded  nodules  began  to  form,  thinly  scattered  on  the  sur- 
face of  the  cathodes.  As  the  electrolysis  continued,  the  bright 
color  of  the  deposits  gradually,  but  slightly,  changed,  and  began 
to  appear  more  and  more  dull.  Toward  the  end  of  the  run  the 
surface  of  both  deposits  became  quite  dull.  In  the  case  in  which 
gelatine  and  hydrochloric  acid  were  added  to  the  electrolytes,  no 
such  action  was  observed  and,  on  the  contrary,  the  deposits  were 
brighter  and  more  smooth  throughout  the  electrolysis. 

Deposits  no.  I  and  no.  2,  as  shown  in  Photograph  XIII.  A.,  that 
is,  deposits  from  electrolytes  which  contained  as  "  addition- 
agents  "  peptone  and  hydrochloric  acid,  were  exceedingly  hard, 
coherent,  but  rough,  and  of  dull  color.  They  were  composed  of 
fine  grains,  but  large  rounded  nodules  scattered  over  their  surface. 
The  bending  test  showed  that  the  ductility  of  these  two  deposits 
was  inferior  to  that  of  those  deposits  which  were  obtained  from 
electrolytes  containing  peptone  and  sodium  chloride,  as  the  test- 
strips  were  broken,  when  they  were  slightly  bent.  The  impurities 
in  the  deposits  were  low. 


56  ELECTRO-DEPOSITION  OF  COPPER  FROM 

Deposits  no.  3  and  no.  4,  that  is,  deposits  from  electrolytes 
containing  gelatine  and  hydrochloric  acid  as  "  addition-agents " 
were,  however,  satisfactory;  they  were  bright,  and  fairly  smooth, 
solid  and  coherent.  The  bending  test  showed  their  ductility  to  be 
very  low,  about  the  same  as  that  of  no.  i  and  no.  2  of  this  experi- 
ment. The  purity  of  the  deposits  was  high,  as  shown  in  Table 
XIII.  A. 

The  results  of  this  experiment  show  that  the  combined  "  acldi- 


tion-agents  "  of  peptone  and  hydrochloric  acid  had  a  somewhat 
similar  behavior  as  combined  peptone  and  sodium  chloride,  but 
proved  less  satisfactory  and  less  effective. 

The  combined  "  addition-agents  "  of  gelatine  and  hydrochloric 
acid  were  very  effective  in  improving  the  physical  properties  of 
the  deposits,  and  preventing  the  deposition  of  the  impurities,  but 
were  not  so  effective  as  the  combined  gelatine  and  sodium  chlor- 
ide, which  proved  the  most  satisfactory  and  suitable  of  all  the 
combined  "  addition-agents "  which  were  employed  in  these 
experiments. 


ELECTROLYTES  CONTAINING  ARSENIC. 


57 


Experiment  XIII.  B. 

In  order  to  see  if  the  addition  of  sodium  salts  which  consists 
of  an  oxidizing  acid  radical,  to  the  electrolytes  would  produce 
any  bad  effect  upon  the  copper  deposit,  this  experiment  was  per- 
formed with  electrolytes  containing  1.5  per  cent,  arsenic,  as 
arsenic  acid  and  the  same  proportions  of  cupric  sulphate  and 
sulphuric  acid  as. in  the  previous  experiments.  The  sodium  salts 
tried  were  sodium  chloride,  sodium  nitrate,  sodium  chlorate,  and 
sodium  borate.  The  amount  of  salt  added  to  the  electrolyte  was 
such  that  it  contained,  in  each  case,  o.oi  per  cent,  sodium.  The 
results  are  given  in  Table  XIII.  B.  and  the  character  of  the  de- 
posits is  shown  in  Photograph  XIII.  B. 

With    sodium    chloride    in    the    electrolyte,    the    deposit    was 

TABLE  XIII.  B. 

Time  of  Experiment  104  hours.  Distance  between  Electrodes  1.75  inch.. 
Current  Density  40  Amp.  per  square  foot.  Electrolyte  contained  15  per 
cent.  CuSOi-sHaO,  10  per  cent.  H2SO4,  and  1.5  per  cent.  As  as  HsAsCX. 
Temperature  of  Electrolyte  50°  C.  Anode  contained  1.30  per  cent.  As 
and  1.27  per  cent.  Sb. 


No.  of 
Cells. 

Addition-  Agents. 

Average 
E.M.F. 
in  Volt. 

Impurities  in  Deposited 
Copper. 

Photo. 
XIII.  B. 

0  As. 

*Sb. 

I 

o.oi  per  cent.  Na  as  NaCl 

0.40 

0.0009 

0.0002 

I 

2 

o.oi  per  cent.  Na  as  NaNOs 

0.42 

O.OOlS 

0.0002 

2 

3 

o.oi  per  cent.  Na.  as  NaClCs 

0.41 

0.0019 

0.0004 

3 

4 

o.oi  per  cent.  Na  as  Na2B4O? 

0-45 

O.OOIO 

O.OOO2 

4 

lustrous,  perfectly  smooth,  solid  and  coherent,  and  was  composed 
of  crystals  with  sharp  edges,  while  the  deposits  formed  from  elec- 
trolytes containing  sodium  nitrate,  sodium  chlorate,  or  sodium 
borate  were  also  satisfactory  and  similar  to  one  another  in  char- 
acter. They  were  bright,  solid,  smooth,  coherent,  and  finely 
crystalline,  though  at  the  lower  corners  of  deposit  no.  3  were 
formed  a  few  large  nodular  crystals.  As  to  the  ductility  of  these 
four  deposits,  those  obtained  from  electrolytes  containing  sodium 
nitrate,  sodium  chlorate,  or  sodium  borate,  were  ductile,  as  the 
test-strips,  when  beaten  double,  did  not  break.  The  test-strip  of 
the  deposit  from  the  electrolyte  containing  sodium  chloride 
broke,  when  it  was  hammered  double,  and  its  fracture  appeared 


58  ELECTRO-DEPOSITION  OF  COPPER  FROM 

fibrous.  The  purity  of  all  the  deposits  was  exceptionally  high,  as 
may  be  observed  in  Table  XIII.  B. 

During  the  electrolysis,  the  potential  difference  in  the  case  of 
sodium  borate  was  noted  to  be  little  higher  than  that  of  the  rest. 

According  to  the  results  obtained  from  this  experiment,  the 
sodium  salts  consisting  of  an  oxidizing  acid  radical,  such  as 
those  mentioned  above  do  not  appear  to  exert  any  injurious  influ- 
ence upon  the  deposited  copper,  when  present  in  small  amounts. 
On  the  other  hand,  they  show  themselves  to  be  beneficial  "  addi- 
tion-agents," instead  of  detrimental,  as  it  was  found  that  they 
improved,  to  a  considerable  extent,  the  chemical  as  well  as  the 
physical  properties  of  the  deposited  copper. 

CONCLUSIONS. 

The  experiments,  as  performed,  may  be  grouped  under  four 
main  headings :  ( I )  Impure  electrolytes,  which  contained  no  "  ad- 
dition-agent." (2)  Impure  electrolytes,  which  contained  in- 
organic "addition-agents."  (3)  Impure  electrolytes,  which  con- 
tained organic  "  addition-agents."  (4)  Impure  electolytes,  which 
contained  organic  and  inorganic  "  addition-agents." 

With  electrolytes,  which  contained  no  "  addition-agent,"  much 
arsenic  and  antimony  was  deposited  with  the  copper,  even  when 
the  electrolytes  contain  1.5  per  cent,  arsenic.  With  electrolytes 
containing  2  per  cent,  and  3  per  cent,  arsenic,  a  still  greater 
amount  of  these  two  impurities  were  deposited  with  the  copper, 
and  large  dendritic  "  trees  "  also  formed  on  the  surface  of  the 
deposits.  These  impurities  rendered  the  copper  dull  colored  and 
brittle. 

At  temperatures  between  50°  C.  and  60°  C.,  and  with  elec- 
trolytes containing  over  6  per  cent,  arsenic,  the  arsenic  acid  ap- 
peared to  act  as  an  "  addition-agent,"  as  it  prevented,  to  some 
extent,  the  deposition  of  the  impurities  (arsenic  and  antimony) 
with  the  copper,  and  also  retarded  the  formation  of  dendritic 
"  trees."  At  temperature  of  40°  C.  and  below,  however,  this  ac- 
tion of  arsenic  as  "  addition-agent "  in  the  electrolyte  did  not  ap- 
pear to  take  place  in  the  electrolyte  containing  under  6  per  cent, 
arsenic,  whereas  in  the  electrolyte  containing  8  per  cent,  arsenic, 
the  deposited  copper  was  purer,  brighter,  more  solid  and  coherent, 


ELECTROLYTES  CONTAINING  ARSENIC.  59 

and  less  brittle.  This  shows  that  the  good  effect  of  arsenic  acid 
depends  not  only  upon  the  temperature  of  the  electrolyte,  but  also 
upon  the  amount  which  is  present  in  the  electrolyte.  This  phe- 
nomenon cannot  be  explained  from  the  data  obtained  in  these  ex- 
periments, but  it  may  be  attributed  as  the  result  of  hydrolization, 
which  converts  the  arsenic  sulphate  (As2(SO4)3)  into  arsenous 
acid  (H3AsO3)  and  sulphuric  acid  (H2SO4). 

Reaction:  As2(SO4)  plus  6H2O     2H3AsO3  plus  3H2SO4 

Temperature  and  the  amount  of  arsenic  in  solution  both  appear- 
ing in  this  case  to  be  functions  of  the  reaction.  As  the  arsenic  is 
in  the  form  of  an  acid  radical,  it  would  not  be  precipitated  on 
the  cathode,  but  would  act  as  a  reducing  agent  in  the  electrolyte, 
and,  thereby,  give  results  similar  to  those  of  the  ordinary  "  addi- 
tion-agents." 

Hydrochloric  acid,  sodium  sulphate,  aluminium  chloride  and 
sodium  chloride,  all,  when  present  in  small  amounts,  have  a  dis- 
tinct action  upon  the  improvement  of  the  deposited  copper,  both 
chemically  and  physically.  They  cause  the  deposits  to  become 
more  or  less  smooth,  dense,  pure  and  free  from  "trees."  Of 
these  inorganic  "  addition-agents,"  the  best  and  most  effective  is 
sodium  chloride ;  hydrochloric  acid  to  a  slightly  less  degree.  The 
effect  of  sodium  sulphate  is  still  less;  it  produces  little  or  no 
effect  if  present  in  too  small  amounts,  especially  at  temperature  of 
40°  C.  and  when  the  electrolyte  contains  3  per  cent,  arsenic. 
Aluminium  chloride,  though  it  improves  the  copper  deposits  to 
some  extent,  does  not  seem  to  be  a  suitable  "  addition-agent," 
while  aluminium  sulphate  is,  on  the  other  hand,  a  satisfactory  one ; 
it  causing  the  copper  to  deposit  low  in  impurities  and  more 
ductile. 

From  the  results  of  the  trial  of  the  inorganic  "  addition-agents  " 
it  appears  to  be  true  that  the  salts  of  those  metals,  which  stand 
by  far  higher  in  the  E.M.F.  series  than  copper,  are  generally 
satisfactory  "  addition-agents."  They  possess  the  property  of 
preventing,  to  a  considerable  extent,  the  deposition  of  arsenic  and 
antimony,  and  the  formation  of  "  trees."  The  latter  action  of  in- 
organic "  addition-agents  "  is  difficult  to  explain,  but,  according  to 
Edward  F.  Kern,13  it  is  due  to  the  reducing  effect  of  these  metals 

13  T.  Am.  EL  Chem.  S.}  1909,  Vol.  15,  p.  473. 


60  ELECTRO-DEPOSITION  OF  COPPER  FROM 

(in  ionic  state).  The  higher  that  the  metal  of  the  "addition- 
agent  "  stands  in  the  E.M.F.  series,  the  purer,  smoother,  and  less 
brittle  the  deposit  appears. 

Temperature  plays  an  important  part  in  the  electrolysis  of 
copper.  With  higher  temperature,  the  ductility  of  the  copper 
seems  to  be  increased,  and  the  potential  between  the  electrodes 
decreases.  In  the  case  of  sodium  sulphate  as  "addition-agent," 
with  higher  temperature  it  becomes  more  effective. 

In  the  case  of  organic  "  addition-agents,"  both  gelatine  and 
tannin  produce  a  remarkably  beneficial  effect  upon  the  copper  de- 
posits and  are  satisfactory  "  addition-agents."  The  presence  of 
gelatine  at  the  beginning  of  the  electrolysis  has  the  effect  of 
causing  the  formation  of  small  fern-like  "  trees,"  but  after 
operating  for  a  period  of  time  the  deposits  are  smooth  and  ductile. 
Peptone,  unlike  gelatine,  exerts  a  detrimental  influence  on  the 
deposits  and,  therefore,  is  an  unsatisfactory  "addition-agent." 

To  explain  the  good  and  bad  action  of  the  organic  "  addition- 
agents,"  mentioned  above,  is  of  no  easy  matter,  as  their  chemical 
structure,  except  tannin,  is  not  yet  fully  and  definitely  known.  It 
may,  however,  be  of  value  to  cite  their  properties.  Tannin, 
C12H3(OH)3(COOH)2,  possesses  characteristic  acid  properties 
and  contains  three  hydroxyls  per  molecule.  Gelatine,  whose 
chemical  structure  is  not  yet  fully  known,  is  also  essentially  acid 
in  character,  as  it  possesses,  when  pure,  an  acid  reaction  and  dis- 
sociates carbonates. 

"  Peptone14  is  of  two  kinds,  which  differ  from  each  other  in 
one  molecule  of  H2O.  Their  chemical  composition  may  be 
shown  as  follows:  C22H34N6O9  and  C22H36N6O10,  the  former  is 
called  A-peptone  and  the  latter  B-peptone.  Peptones  are  pro- 
nounced acids,  which  redden  litmus  paper  and  which  form  salts 
with  carbonates  after  having  expelled  the  carbonic  acid  gas ; 
adopting  the  simplest  formula,  peptones  are  monobasic  acids,  but 
such  a  simple  formula  has  to  be  multiplied." 

The  deposits  of  copper  obtained  from  electrolytes  containing 
the  combined  "  addition-agents  "  are  all  satisfactory,  particularly 
when  the  combination  of  gelatine  and  sodium  chloride  is  used. 
The  striking  effect  of  the  inorganic  substances,  when  present  with 
the  organic,  is  that  it  counteracts  the  bad  effect  of  the  latter.  Of 

14 "  Chemistry  of  Proteids,"  Mann,  p.  188. 


ELECTROLYTES  CONTAINING  ARSENIC.  61 

the  two  inorganic  compounds  (sodium  chloride  and  hydrochloric 
acid)  that  were  used  for  the  combined  "  addition  -agents,"  sodium 
chloride  is  in  every  case  better,  more  satisfactory,  and  more 
effective  in  producing  good  copper.  This  shows  that  the  better 
effect  is  due  to  the  presence  of  sodium  ion  in  the  electrolyte.  As 
evidence,  a  particular  case  may  be  cited,  that  is,  a  case  in  which 
peptone  and  sodium  chloride,  and  peptone  and  hydrochloric  acid 
were  used  as  combined  "  addition-agents."  The  copper  deposits 
obtained  in  the  former  case  were  found  better,  both  in  physical 
character  and  in  purity. 

In  considering  what  has  been  said  above,  the  questions  may  now 
arise:  What  causes  the  organic  compounds  to  behave  so  differ- 
ently in  the  electrolytes  when  an  addition  of  a  small  amount  of 
either  sodium  chloride  or  hydrochloric  acid  is  made?  Does  the 
presence  of  either  of  these  two  inorganic  compounds  cause  the 
organic  ones  to  undergo  a  chemical  change?  These  questions 
cannot  be  answered  without  special  investigations  and  are  not 
within  the  scope  of  the  present  research. 

With  the  results  that  have  been  obtained,  and  with  the  effects  of 
various  "  addition-agents  "  that  have  been  tried,  this  may  be  said : 
the  combined  "  addition-agent "  of  gelatine  and  sodium  chloride, 
when  present  in  a  small  amount,  proves  to  be  the  most  suitable 
and  most  satisfactory  "  addition-agent "  for  copper  sulphate  elec- 
trolytes containing,  especially,  a  high  proportion  of  arsenic,  as  the 
deposited  copper  possesses  the  greatest  ductility  and  the  highest 
purity. 


62  ELECTROLYTES  CONTAINING  ARSENIC. 


VITA. 

Ching  Yu  Wen  was  born  on  the  i6th  day  of  December,  1881, 
in  the  city  of  Canton,  Kwangtung  Province,  China.  He  studied 
the  English  and  the  Chinese  languages  in  Pei  Yang  University, 
Tientsin,  and  there  prepared  himself  for  entrance  to  the  American 
institutions  of  learning.  In  the  year  1904,  he  entered  the  Massa- 
chusetts Institute  of  Technology,  to  study  metallurgical  engineer- 
ing under  Professors  Robert  H.  Richards  and  Heinrich  O.  Hof- 
man,  and  was  graduated  in  1908.  In  1909  the  degree  of  Master 
of  Science  was  conferred  upon  him  by  the  same  institution.  Con- 
jointly with  Professor  H.  O.  Hofman,  he  published  an  article  on 
the  "  Heat  of  Formation  of  Some  Ferro-Calcic  Silicates  "  in  the 
Transactions  of  the  American  Institute  of  Mining  Engineers, 
July,  1910.  He  entered  Columbia  University  in  September, 
1909,  and  studied  metallurgy  in  the  School  of  Mines. 


AN  INITIAL 


To  •      sr. 


LD  21-!OOm-7, '40  (6936s) 


